BULLETIN OF THE GEOLOGICAL SOCIETY-OF CHthAVoL. XXH, P40. 13j PP. 2147, Juwe. 1942

Reflections.f t Years' Experilnce*

By

J S. LEE

Chairman at the Jutilce Meeting

for the Twentieth 1nniuersary

of the Geological Societ'

oJ China

When .1 was called to deliver an address to tuis cominctnorabk gathering¡ made some eort, following thc usual practice, in the choice of a suitable subject.Before, however; I could setíle down seriously on geological problems I found itdiflicult to resist certain distrations that arise from the development of scientiftorganizations in this country. Involved aiid diversified as these wanderia;thoughts nmy be, you may, with toleration, grant Inc a few moments in disposíngof these apparently extraneous matterr, for the way to kaowlcge is sometimf sno less important than knowledge itself.

Among the number of scientific Societies that have sprang up in recent.years throughout China ours will probably be counted as one of the forerunners.But as compared with the sister institutions in otherk lands our Society annotbesaid to have advanced much beyond the juveilc stage. We have endeavotuedto adapt oirsclves to this new frrn of intellectual activity as thozgh we hayclanded ourselves in an utterly strange world which has nothing, in common withthat in whicb our forefathers struggled for many centuries. It cannot be gainsaid.that we are marching into a field which is entfrely new, and the method and

'In the absence of Dr, Lee, this address was read hi Dr. Ching-yuan 'Y. Li befgec the bilesMeeting on March 20, 1942.

22 ßiilktir; of ehe Geoocq1 Society of Ciiii

objective of enquiry are soinehing unknown before. When, however, we searchk-r the profounder basis on which varieties of man's intellectual activity rests

we begin to disóver certain signs which disclose, in some rneasúr&, our predisposition in modern scieñific' effort not "tnconnected with an 'age-long culturalhistory. With thai historical background we suffer from certain drawbacks, andat the same tithe are endowed with certain privileges.

In making a stock-taking survey of the matrials which constitute our

humble contribution for the last two decades 'you cannot avoid to notice the

extraordinary fact that how few is the number-of papers dealing with the economîaspect of geology that appeared in th,e Bulletin of this Society. Among the reasonsto account for this record T would point out one; namely, that non-utîlitaria

.andency has always constituted a strong trait in the character of Chinese intel-

ligentsia throughout historical times. Th cy against science misma-naged. as theresult of the perverted development of:modern materialism, is thus a voice thatnarticularly rings high in our mind. It is not my object to evaluate this tendency,but merely to suggest that we will do swell -to exercise occasional introspection.

Suck handicaps as duo to the absence of any geological legacy,. so tspeak, sometimes. twn ot to' be an advantage. The formidable: load f :tradi_

tionrlism 'often witnessed in the Western scientific world, while serving to-

stabilize scientific thoughts and procedure, has beèn now and then not eiitireI?ree fron adverse effect upon progress: The issue between the Plutonist5 andNeptunists or that :betwcèn catastrophism and- uniformitarianism was eventuall!settled rightly: ßut considering the brilliant mind that were entangled hopelesslTa:i uselessly in views and channels of thoughts that were destined to he-

discarded we must admit that that was a loss of the time: Geology has now

advanced so far, sse need not pay serious attention to such esents save for

historical interest New- problems of comparable magnitude have however arisen,and will probably continue to arise as our enqu&y is carried on further andfurther: Here a severe demand is laid on our open-mindedness, care adconstructive genius. -- As "free-thinkth' unhampered by traditional concepts,we' are happily placed in a favourable position to usher in any new ideas if

they rest- on a sound basis.

Theie was a time when the great masters 'of ir science in. the West

had to faces the challenge of. the church er the reverse. The disreputable attcks

Lce:Rej7cctions 012 Twenty Ycar' E.vperience 2

from the doctrinaires spread, at times, so far into tho sociai stratum that theybrewed to a tempo little short of ostracism. It could riot be a plasan.tsituation when we come t realize it, nor could it have been in favour of trueprogress. That age is fortunately gone by. And wç in this country have neverhad the least notion of what such an ostracism amounts to. The new challenge,

it is said, now does not come from the church but from the state in certaincountries Follosnng the totalitarian logic I presume tint geologists are to beregarded as bot living mechanisms that should be controlled and handled by thestite as a sort of "divining' device for opening natural resources oq theexigency of the state more particularly for the purpose of prosecuting war andconquests. It is now up to us among the. scientific wotkers in the world, todecide whether we would, with docility, come under the yoke or to stand

boPlly. on the paths of intellectual freedom. After a sanguinary struggle formore than four and halt years it is row perfectly c'car that we, in among afamily of freedom-loving peoples, have usiswervingly stood and will always stàndfor our cause,

Our society, though carries the usual . banner of a national organization,is in fact international in character. You. need only turn over the pages onwhich the names of our members are printed. They come from all laads, andactively participate the work here in a fraternal atmosphere that, as far as I ca ngather, is sldorn so widely and deeply felt in many of the similar organizationsin other countries. In this, I do not mean it should be pointed out, that thereal spirit that promotes scientific organizations of hih standing. in other

countries has any xenophobic tendency. It is rather the subtlety in the shadesof differeñces between the racial or national barrier that tnakes the foreignersshy and feeling less at home than the majority who talk in a language otherthan their own. Again, scientific organizations in the West have largely growrup around local centers. Each of the groups has its own tradition which, whenbrought together, nccds some delicate and careful adjustment. Conscious efforts

have been made by many ef the societies as shown by the invitation of foreignmembers. Yet it is still questionable whether such artificial methods havesucceeded in breaking through completely the subtle differences. Happily wjrii

our society, and thanks, to our cultural tradition, no stich differences have ever

entered our circle at the very outset There is no room for any pettiness ofniijicl to play, nor any prejudice to combat against. We have ever adopted

24 Bulletin e'f the Geological Society of Chs!:a

hc leading Western languages, principally English, as the offici?l means ofcommunication, not without sorne sacriee on our own convenience.

These matters of fact, for that express the attitude with which weregard the matter, would nt be worthy of mentioning in normal times.in times as these when wr see thàt she human family among the ever-lastingebb and flow of faunas throughout: cons of ages, in which it plays but anephemeral part, has come to a stageof unprecedented: cataclysm not through thegrim forces ot nature, but of our own doing, edch of those who daim to playapart in men's intellectual activity should spare sorne constructive effort for thesake of cultivaing intellcctsal fraternity The sais age of Tomo sapsen is

ceitainly not a problem for the geologist, and still lcss tor the few of isis who

happen to meet here today. But as individuals groping in the drknss withthe only safe guide :of intelligence and assessed knowlodge, we ought, :fl theleast, prove our sapient qualities within our, own domain. Knowledge holdsthe key; and the way to knowledge, may I repeat, largely decides the' issue:.

Now we will come. closer to geology. Instead of focssing our attentionon sorne special problem it may be' apropos in a meeting of this nature, if Iwere to call your attention to certain points that geOlogists working in thiscountry, or in some cases at large, arc apt to forget, ileglect or decry theirinterest from a professionaF stand-point. Problems often aise which are not somuch concerned with th'technical aspect of the treatment, but rather: with theinterpretatIon of: the facts. And on the interpretation ofen hangs some cardinalissue. Usually little difficulty is felt in accepling : funclamen,tal principles Oncelaid down. It is, hOwever, another matter tq observe faithfully those principleswhen we corne to practice.

The possibility and limitation in exploring fossils as effective means cfstraigraphical classifiation and correlation are geperally well understood.Sufficient care is not,: howevér, always xercised in thir stratigraphical eva1iations they are found.- When we realize how minimal is the proportion of thergansms once lived that happened to be buried in the rocks and preserved as

fossils, and how minute is the fraction of the fossilized orgaûisis happens to bebrought. to our nptice, there is no escape from the conclusion that in any strictcorrelation solely based on fossils we are dealing with a problem of prçbabi4ity.It is hardly necessary to add that fossils are not the oniy means to that enJ.

.Lce:Reflectons on Twenty Years' Experience 25

The point that needs careful consideration is the zoial value which is now andagain assigncd th a given organic form that after a long and eNtelasive srchmight turn out to be possessing a long range. As significant ezamples I mayref er to the tabulate coral Tetra porn, well known for a utnber of years as atypical eleiñrnt in the Chihsia fauna of Permiso age, was actually found in theLower Carboniferous, sod to number of species of fusulinids that were allegedto be arranged in zones, but hav proved to be of no zonal value. These

lessons suffice to show how utmost precaution is needed in dealing with a fewfossils coIleecl in a succession of strata from a limited area.

Still more amazing is the find from the top of the Wutung Sandstoneof the Lower Carboniferous at Lungtan where Sphenophyllisni of the type ofS. thoii hitherto entirely unknown below the Stephanian of Europe. I had anopportunity to examine the locality with care, but failed to find any tectonicreason td account for this extraordinary fact. A recent case concerning theoccurrence of characteristic form of Upper Devonian fish, Bothriole pis,- in whatappears to be a series of continental beds forming the lower part of the MiddleDevonian in central Hunan is no less astonishing. In this case funber ínvestigaticnis however still xeeded. More fin.ls of similar nature can be brought foh. ltwould appear from such cases that we must guard ourselves against any hastyconclusion in estimating the true stratigraphical value of fossils found in positionsstrange according to an established scale. Nevertheless, isv view of the vastamount of sifted material and seasoned data that have accumulated in the domainof stratigraphy there i no room whatsoever to cast any dnubt opon the sequenceof the malor formations based on the record of advancing life-forms.

With the advancement in recent years in palaeontological methods,

particularly in the elucidation of the internal structure of groups of invertebratesby serial sections, wç are enabled to come to a closet understanding of the livingorganism that once inhabited the xsard parts. It turns out that many widdydivergent forms can pssess similar external appeafancc Thus, not only theirrespective value as time-markers can be differentiated, but also the phylogenichistory of a particular group may be more fully explored. Inspite of the largeamount of införmation thus wrought out, the prolilem still remains why theperceptible variation -within a species or between the allied species is of ten

exhibited by an assemblage of fauna, while the links between dierent gene-a,

26 Bulletin of the Geological Society of China

or ti1l more, between different families are larglv missing. Those who havehad some eaperience in dealing with fossil faunas must have been impressed withthe fact that many of the leading groups of organisms look as if they suddenLyappear in a formation and die out with equal abruptness. It is easy to

understsnd why they might suddenly die out, but it is not so easy to visualize

why the prototypes are so often not represented by a linear series of forms. The

absence of record or the assumed precence of an unknown nursing basin do notseem to be an adequate expinatin in all cases.

Another aspect of modern research ensuing largely from the growth ofpalaeontological knowledge is the fascinating subject that came to be known aspalaeogeography. The numerous maps that have been constucted on th basis

of the distribution of different faunal elements in a givcn period, even if oftentative nature, afford a üseful service in many lines of studies that are connectedwith the broader features of the earth's surface. A note of warning must,however, be added in constructing or using such maps; for before an exhaustivesearch is made, the absnce of certain faunal elements in a region can often beconstrued on a variety of circumstances. The validity of a land-brrier constructedon that account must be qualified by the extent to which the relevant faunalassemblages have been collected no less than by the distinctive characters of theseveral faunas already in hand. r may mention one case of interest. It has beenknown for a long time that Aclinoceras stands as a leading element in the

Middle Ordovician fiunà of northern China, whereas Orihoceras plays a dominantpart in the contemporary fauna of the south. It was therefore suggested, andindeed believed, that g land barrier more or less corresponding to the presentTsinling and its astern continuation served to sever their intercommunication.

Two years ao I found, hQwever, a fine specimen of Actii2oceras in the

neighbo.urhood of the Chienkiang city, south-eastern Szechuan. What then

höu4d be the conclusion to he drawn from this new find? Arc we to suppose.that a narrow gap is left in the assumed barrier for occasional incursions of thenorthern fauna or to attribute a peculiar hábitat to the south that did not favoura development of Actinoceras as flourishing as of Orth oceras?

The use of fossils is sometimes urged as indicators of past climates. There

cois be hardly any doubt about the habit of many of the Quaternary and evenFHocene forms, for they can be readily compared with their living allies. But

Lee:Refiectiorzs 012 Twenty Vcrs' Experienc: 27

the more rcmote we go along the scale of time) the less certain Lecomes theparallelism or analogy to b drawn from living organisms Al!owng time, therange of adaptation, especially of the lowly organized forms, is a problem thatseems worthy of further itivestigation. Meanwhile climatological deductions from

the record of past faunas and floras might be preferably con-sidered in conjunction with the nature of deposits in which they occur.

This raises the abstruse subject of sedimentary petroraphy, In spite of

serious attempts that have been made by a nufnber of authoritïes an the subjectwe cannot yet say that there has been. much progress in the way o systematic

treatment. True, detailed studies on the grade, size, shape. and arrangement orpacking of the constituent grains of sediments, tracing of their original sources,

determination of certain significant mineral species, analysis of heavy mineralsenquiries into the conditions which control the precipitation either nf colloids or

of dissolved matter, demarkation of facies, estimation of the lateral variation ofthe thickness of certain type of deposits in terms of "Isopackytes'' -and so forthhave all afforded some help in the interpretation of the "geologicai document",but as regards the proesses and circumstances, both original and secondary,connected with the transformation of the mineral matter in the sediments wemust confess our ignorance in the majority of cases. You cannot fail to realizehow little is the attention we have paid to this rich store of information whenyou come to review the large number of stratigraphical papers published in ourBulletin. The description o sedimentary. rocks is usually summed up in suchbrief terms is sandstones, shales., himestones and the like. Even with the methodsavailable and knowledge in hand, ve can certainly go a step further.

Nor has our attention been duly directed to' the igneous bodies both -inthe field and in the laboratory Petrogenesis has made a long stride, as aconsequence of intensive studies in the field on the. facial characteristics of theindividual and connected igneous masses or suites, their probable differentiationunder various and varying conditions of pressure, ternperature and proportionalconcentration in space ancl possibly in time as well as of the results obtainedfrom synthetic experiments on silicate-melts.. By linking up the latter aspect ofresearch with physical: chemistry principles of fundamental importance become atonce available, notably those connected with the phase rule. Those -of us whoare disinclined to secure a command of knowledge of that endless varieties ofg1cous rocks would probably recall how we were bored at times by mere

28 Bulletin of the Geological Society of China

descriptions of mineral aggregates with shades of textural difference undernomenclatures not particularly attractive, but little beyond. Modern petrologyoffers however many redeeming features. Around those recondite names of rocksnow cintres a lively, interest. The new sience of petrology, it is perhaps no.exaggeration to say, is not only concerned with the natural history of igneousrocks, but is intimately bound up with the. major problems of geotectonics andthe crustal structure of the earth in general.

Scarcity of petrological contribution from members of this Society can hardlybe e:e.used on te grounds 'of lacking of material of fields. The large iCtrusive

masses ranging from granites to quartz-diorites and their differcntiatcd associates,with which the whole country is studded, the batholiths of MongoIia the

numerous hypabyssal sheets in nearly all the mountainous areas, the volcanicflows f 'Sinian, Permian and later ages with associated pyrociastic material, thesporadic appearance of alkaline rocks in Shansi, and the extcflsive belt of igneouscomplex along the south-eastern and southern coastal districts all offer prolkmsof first-rate importance that ttill await us to explore.

To cope with new puoblems it is orten expedient -to try new methods. Asa matter of passing interest, I may inention one designed to render some help.tu the study of igneous bodies as they occur in nature. It was suggested thatsilica, both free and combined, might afford a clue that discloses the mode ofdifferentiation of a large intrusive body as well as those occurripg in isneighbourhood with apparent subterranian connection if points of equal concentra-tion be connected by lines separated by definite intervals. Such lines, termedthe "isomarths", might- then represent the chemical contour or gradient of thedifferentiating mass. With the mode of vOriation thus graphically determinedw have at least -established one step from which further enquiries may be madeinto the conditions governing the differentiation. Isomnarths of other kind mayalso be constructed, such as those based on -the concentration of some keyelements other than silica or of some key minerals as the petrologist requires.Their ialae would be qualified by the degree 'of inportance which the sevcrlchemical or mineral constituents play in discios-ing the genetic history of a

particular mass. ?Ihis method was twice tried out in the fleld in connexionwith a survey of Certain ''diorite" bodies, in one case the isomarths actuallyyielde?l some evidence 'for but a remote Felation between the main mass and anapparent off-shoot lying nearby; and in another rh abrupt termination - o the

e:_Re7cccio;is on Ttvcty Yearf Execrience 29

ïsctmatth led to the discovery of an important fracture within the igneous body.it seems that some such a method when improved cart be applied with advantagein the systematic survey of certain types of igneous rocks.

(3f the major problems in geology none seems to have aroused in recentyears so wide an interest or such heated discussion as those belonging to thedomainof geotectonics or dynamic geology. A moment ago I referred to the viewsof the Plutonists and Neptunists and the doctrines of catastrophism and uniformita-.rianism as fundamental issues in the history of geological thoughts. If we may,look upon any modern geologica' development as issues rivalling these in importanceand magnitude I am inclined to suggest that they, are the hypotheses or problemsconcerning orogenesis and the question of mobility of continental masses eachas a whole or as integral parts of the crust of th earth; Views held by,geologists on these questions are, so widely divergent or even hostile that it is

sometimes diflcu!t to find any common grounds. Stark conservatism may meanmrnunity to any new conception hçnveyer enlightening: Ready inveition, on

the other hand, of hypotheses ad ¡zoc possibly leads to chaos, In the intere ofthe advancement of knowledge the latter seems to b the lesser evil, for howeverwild a hypothesis may he there is no escape from the final judgment of fa'cts

Thanks to the memorable contributions made by those pioneers such as

Purnpelly, Richthofen, L'oczy Obrutchew, Willis and Blackwelder and a numbèrof others and to the efforts of the Geological Survey änd of other institutionswe may claim a skeletál knowledge as to the major structural pattern of thiscountry. At the same time we must admit that much of the structural detailsof this com?lex region still remains inaccessible: It is imperative to çonfessthis truth because, on the one hand, we may thus appreciate the attractive natureof the field and the value of tie facts to be wrought out with adequate care,and on the other, gauge the accuracy of the published maps: Years ago ageological map of South China was brought to my notice, gorgcousl coloured,and published by a foreign institution. Even the larger units of the stratigraphof soithern China was at that time scarcely known. How cart you then expectsuch a map to rprescnt even a shadow of truth? It is indeed difficult to

understand the real purpose for publishing a map of. that kind. We ourselves

are of course to some extent to blame, for the absence of authoritative mapsleaves a breeding space for such indignities:

SO balielzc of the Geological Scciety of Chinc

Detailed mapping, it. is hardly necessary to say, is the first step towards

the understanding of geological structure; and the acquirement of adequatestratigraphical knowiedge must precede any large scaled mapping. In dealingwith extensive areas geologically almost unknown, as often is the case when weset out into the field, it seems to be a wise pian if we proceed first of all to selecta number of suitable localities where we may concentrate our effort in workingout the stratigraphical succession with a vigilant search not only directed to theorganic remains contained in the different formations but to the possib1e breaksbetween them. Such localities may well be regarded, so to speak, as strategic

[x)ints. A nere covering of areas with a diffused effort often means a loss ofthne and labour:

In the early days when the Icading geological institutions in this country.

and most of us who had an active interest in held-work were largely stationedin the North. The comparatively simple stratigraphy and apparently simple.tectonic relations between the various formations gave us the general impfessionthat, apart from the mountainous regions) this continental country was essentiallycharacterized by a stable continental structure. As the range of our explorationwidened to the South, a very different state of affairs gradually forces it9elfupon our notice. Here we -arc not only brought lace to face with nunerousfossiliferous marine formations, interformational breaks and unconformities ofviolent nature unknown in the North, but arc. frequently concerned with

exceedingly complex structural relation. k fact tectonic problems balk largelyall over this regior

With such complex problems in hand we will do well to proceed, withthe greatest caution. Iñ any analytical study of tectonics the temporal aspect isno less important than the spatial. It might be desirable to formulate our

ctminoIogy accordingly; As a matter of common understanding I would suggesto use some ancient or ill-defined geographical names for denoting the various

epochs of movement; for such a procedure can avoid possible confusion arisingfrom a term in stratigraphy that happens to be derived from a locality where

conditions o coMinuation and cessation of deposition are equally pronounced.

It should be borne in mind that there is not much difficulty in proposinglocal stratigraphical term so long as a satisfactory account is given of a well-

defined series tyjical1y exposed at a locality wherefrom the term is derived. It

Lee.._Reflectio,js on Twenty Years' Eapeience 31

o however anotner matter to coin a new naine for the purpose of marking theepoch of an earth-movement. When a gap is detected between an old and ayoung ormation, it only establishes the fact that there existed conditions o non-

epesition. Emergence can only be proved by evidence of erosion which may ormay not be preceded by mrked folding on the part of the older formation.Wíthi the interval of time unrepresented by- sediments there is nothing againstsis to postulate any number of earth-movements as far as a particular. section is

concerned.. A term proposed to denote an unspecified movement would lose itsmeaninworst than that, would cause confusion. The . propesition f a newterm marking the diastrophic epch must be withheld until a section is hcated,,in which is revealed an interval of erosion suthciently sharp and short as topermit accurate determination of the time when the movement took place. Totrace the erosional surface in the field is often an arduous task especially in placeswhere the beds stand on ends or in gently inclined strata without markeddifference in strike. My own experience in dealing with tho structural relationbetween the Huanglung and Maping limestones in a number of places showsthat traces of the erosional surface can Ofliy be sought within one or two feetor even a few inches from the boundary plane. Even such traces are not alwaysvisible in the weathered exposures. Similar conditions may be expected in therelation between other formations.

As te the stratigraphical breaks which cover, a fairly long interval oftime the interpretation is sometimes put forward, perhaps unconsciously, that thediastrophic epoch immediately precedes the sedimentation of the younger bedewhichdirectly overlay the plane of unconformity. The fallaceous nature of suchan interpretation is generally well understood in theory. But in practice theseal significance of the case is sometimes overlooked. If the formation abovethe plouc of unconformity is marine nothing but a marine transgrèsion is

thereby indicated. And a marincltransgrcssion is something qaitc different froma tectonic movement.

lt would be hardly worthwhile to lay stress on such commonplace as

these had ít not been for the reason that points of fundamental importance areinvolved in these issues at least with regard to the time relation between thenumerous episOdes bf earth-movement.

In the geological maps published in the early days of parts of this countryyou will find surprisingly frw tectonic elements indicated. The principal function

BufieÍ!;2 of tua Geological Society o! Chio

cf a geoioicai map is to show the geological structure of a country. A mapthat falls to isciose the- structural pian with regard to at leaat the majortectonic features would largely miss its object. Twent years' xperietice has.however, taught us to take up a different attitude. Maps published nowadaysshow a considerable improvement. But in some of the large-scale maps thepertinent structural lines are still often not sufficiently clear as to indicate their

inter-rèlation, or in sufficient detail as to afford a basis on which tectonicanalyses may be made. It is of course to be admitted at the outset that not allthe structural details can be crowded in a .single map, however large in scale;

nor can w expect every observer equipped with thc experience to recognize inthe field ail the features there are. The point of primary importance is that n-o

effort should be spared in determining the nature of a given fracturewhetherafault or a thrnt. T ain inclined ta suspect that - sottie of us arc apt to take

these fundamental tectonic elemeats too light-heartcclly. Substantial evidence

is requird before we proceed to draw a line of fault or thrust.

The interpretation in term of geodynamics of a set of tectonic features -

arising from an epísod of earth-movement is clearly a problem that borders ongeology and geophysics. The old naturalists' stand in handling these matters isno longer adequate just. as descriptive -mineralogy falls short in coping withmodern requirement of the knowledge of crystal structure. Departmental knowledgehas now advance to a stage that we haveto oivisage hosts of problems whose -solution needs a joint effort. in the sphere of dynamic geology these problemswhich used to loom far in the horizon have no w drawn so close to us thatunkss w can have them satisfactorily dealt with it seems - difficult to make

- further progress. The helping hands, in this particular braich -of sciectificenquiry, must come -from the physicists. It is anfortunate that geophysicists

often formulate their problems in too simple a manner, and that the- geologistsare liable t'o overtook certain fuhdamental principles velI established -in physical

science. -

A few examples will suffice to show he srious nature of what is impliedin this bold statement. It is not our business to point out where geophysiciststend to err, but it is up to us geologists to expose our own, ignorance or negli.gence. The -principle of isostasy is generally accepted by geologists, and success-fully applied to explaining- the effect of post-glacial elevation in- certain cases.

But when we come to attribuf the additional load of sediments in extensive

Lee :Refiections; on Twenty Years' Experience 33

deltas or in geosynclinal areas as the unique cause of subsidence we step beyondthe range than is warranted by the principle. To hold th slowly accumulatingload, such as provided by ordinary sediments, in a trough as the agenty thatcauses gradual depression of the area covered is an attempt not to prove but todisprove the phenomenon of isostasy, for isostasy requires the relatively lightlyloaded and depressed region to rise as compared with the elevated tracts of land,usually of higher density, lying in the neighbourhood. It is a matter of surprise'to see that geologists of high standing still dwell on this false ground.

Again, the occurrence of an overthrust is usually taken as evidence for

a movement coming froni the overthrust side. There is nothing wrong in thisargument as far as it goes. But when the geologist proceeds to deduce that theorogenic force came from the overthrust side, and sometimes with the furtherdeduction or implication that it came against the inert mass upon which the over-thrusting took place, he violates a fundamental law in mechanic's, of *hich hecannot be excused of being unaware. We have no right to talk of inertness ofany part of the involved mass whenever a translatory movement is in evidence,however slight, And in the case of overthrusting the question essentially hingeson the relative strength of the opposing masses. What ve do know in connexionwith a thrust is the existence of compressive stress that once operated in the direc-tion perpendicular to the thrust plane but nothing further. Unless and until wehave had a complete survey of the distribution of forces or the arrangement ofa system of stresses in the rocks involved we can hardI draw any safe conclusionas to the nature of the earth-movement. It seems advisable to guard againstthese pittalls in deducing the mechanical significance of folds, and faults.

Thus it is evident t'hatthe analysis of complex'stresses as deduced 'froxvarious mechanical:structures of rcks would be an essential step towards the.understanding of, the dynamic signilicance of tectonic features at large. Substanceslike rocks cannot be deformed or shattered unless the stresses: applied exceed acertain limit ccording to ordinary epertence The value of that lumting Stress,or strength, does not only depend on the, .nature,of the stresstensile, compressiveor shearbut on the inherent 4echanical properties of the rock. ' Laboratoryexperiments so far carried, out substantially support this conclusion. In spite of

these experimental, facts' it' is sometimes claimed that rock's,jossess no fiñite strengthand that they may yield 'to any stress,: hóweycr feeble, provided a sufficiently,

long duration is allowed for the.continued operation of the stress. Allege4 bèn4-

34 Bellctin of the Geological Sacie/y of Chine

ing of ancient tombstones and marked-deformation, without fracture; -of- a glasstube -löaded- in the middle partfora number of years may be cited in favour

of this cQntention.

lt is difficult to ascertain the hearsays about the tombstones. Severai strangecases -hnwever came to my fotice in this connexion. Most spectacular of all isa small, lenticular pebble, 35-çm. in diameter and about 8 mm. thick in therniddi, composed ôf a hard, fine-grained quarizitic. sandstone, well rounded inwater and deeply marked on one of the flat faces by parallel striation which appearto be due to the weathered traces Of bedding planes. This pebble is sharply bentin the middk along the directión acros 'thu striations wh.ch lie on th infolded

pide g The bending amounts to nearly 900 without the sligl-'test sigi of fractureas -if the wh'-le' pebble had been made of asry The part of the smooth facewhich is bent over is well grounded and polished with a few faint striae runningnearly perpendiuiarly to the edge 'of the bend. Ir. I. Chang found thi curiousobject in a heap of gravel excavated for building puiposes from a place some ioti to the south-west of the Kweilin Laboratory. Creful investigation showedthat the materiäl was undoubtedly washe& out from the end-moraine lying closeto the locality where the gravel occurred.

..nther piece of hard sandstone, similar in composition, nearly three timesas large as the above-mentioned pebble was foûnd by Mr. Y; -C.- Hsu'in.the same

locality. - It is bent ovtr- 'for almost exactly A deformed 'chèrt pebblè of6 5 to 7 degree in hardness Was noticed by myself at Ankiang, south western

1-lunan. - It was found on' thè rivet bed, presumàbly dérived from th' fluvio-glacial' deposit. This-pebble, well 'worn in water; theasures i cm.- -lon, 6 cm -

bÑad- at the broader --end and about 3.-5-cm.thkk on- the -average. The bending.

which âxñounts to bott ---so°, --occurs abruptl' along -a :th1e about 3 cm.- froth the

hrdder end. .Judging from the ignmetit' f the ihte 'uvd pressmarks-ôn the'othW-ise flat ad smooth -surface it appears probable that the pebble rested on

edges oif a tockf

even superior har4ness while it wás loaded above. - As aresult the ovet.hanging - part yielded to tht 'bending stress. -

Ln these -cases-the-r is h dly any doubt that the' pebbles were once subjected -

to a: stierfidial' load'-bf ice' Ihich could not háve exceedéd â thickness fxoo rn.,probably 'uh less.' The maximtih stess.diffeÉence that outd- have been indutc-

Lec:---Reflcctioas on Twenty Years' Expe'iepce

in the pebble under worst possible condition cannot therefore exceed the order ofro' dynes/cm.2, that is, less than one tenth of the strength of ordinary sandstónesobtaiicd.fróñt laboratory tests. Stilt more important is the fact that the, deformedpieces of rocks reveal no sign. whatsoever of fracti.sre, but were simply bent underconditions that may be closely compared with those of plastic flow.

One more case may be added, that seems to match the alleged yielding oftombstones under . their own weight. On the northern side of the Luling basinin the Lushan a large block of the Niuercheng sandstone about 30. feet long,some 15 feet wide and 8 to 9 feet thick, stood by the side of the house whichJ used to occupy. About three fifths of its length was stuck in the consolidàtedboulderclay, and he other tvo fifths hang in the air, with an inclination ofabout. 300 from the horizontal. The overhanging part described a curious archwith a marked curvature extending into the ground. Atflrst it was thought thatthe dislodged block might. happen to have come from a small anticline' formedin the Niuercheng sandstone before ¡r wastransported to the site where it rested.Exhautive search in the neighbourhood showed, .however, that the tectonic-condi-tions of the wholè area 'did not .admit the existence of such miniature but sharpfolds. Moreover blasting an4excavatioñ revealed a curious, cresdntic cá'iy, aboutknee deep, several fèet long and nearly a foot wide, between the inner side of

the arched rock and a smooth and convex surface of the boulder-clay. The twósurfaces. conformed. in. shape, but the arched inner surface of the kock exhibiteda greter curváture. From these circumstances it appears highly probable thatthe rock gradually yielded to the stress due to its own weight since bôulder-claytimes;

Fron'i these observed facts are we then to draw the conclusion that rocks

possess no finite strength? If such a conclusion be admitted we shall haye totind mountains collapsing' to a sensible extent all over the wórld, and all imperafection of isostatic corn penation disappearing. The fact is however otherwise.The vexing situation mar :be redúced to this: we cannot dens, on the one handsthe deflnitestrength of rocks as obtained from laborâtory tests, and the highlyelastic property of the earth as a whole as demonstrated by the famous MkhelsonGale experiment; and on the other, we have to admit that'rocks doyield to ¿mailsttesses far below their strength under circumstances unconnected with the increasecf temperature.

Bulletin of tke Geological Society of C/2ina

This flagrant contradiction leads us to question our fundamental conceptionregarding certain properties of matter within ordinary experience. We know thatthere are different kinds of solid, and that in the same kind of solid substance

the value of the elastic moduli may vary according as the condition of loading,It is shown, for instance, that granite and marble exhibit a lower young's modulusunder a static than under a dynamic load. The curious behaviour of pitch and toa less notable degree, of such liquivitreous substance as glass, seems to suggest

a point which we usually fall to grasp. Strength may be defitied as the limit-ing stress under which the substance begins to yield more or less permanently.

And viscosity is usually measured by the ratio of the shearing stress to the rateof change of shearing strain. For a given stress the less the rate of change ofshearing strain the higher is the viscosity of the, substance. In ordinary liquids

it is practically impossible jo ascertain the amount of elastic strain, if it exists

at all, because a change is continually, or in, infinitesimally short intervals of

time, taking place in the strain.. The rapid absorption of distortional waves byliquids certainly demonstrates a loss of energy, but it does not necessarily provethe absence of elastic strain even of momentary nature in any part of the liquid.In highly viscous material bórdering on solid, or even in solids, it is.conceivable-that a similar state of affairs may exist, but the rate of change of strain evenwithin the so-called elastic, limit may be so slow that it 'is hardly appreciablewithin our life time. We can use refined rnethds 'to measure the strain, forexample by means of the length of light wave; but we are as yet short of directmeans for measuring such transient elastic strain as- may- have existed--in afraction of a second, or for determining the rate of change of strain due to a

given stress extending over - a period of hundreds of thousands of yeats. Thusthe factor of time appears to constitute the kernel of the problem.

It would be too pretentious t aim at - nal solution of the, problem inThis broad discussion. What I have been trying to do is to find a way to escapefrom the impasse lii ,dealing - with the mechanical properties of materials -. like

- rocks ostensi1y. ass1ernbled through etcrogencous grouping of crystalline- and non-crystalline substancs. - If in this or in any- other leading geophysicists, how thecontinental masSes presumably essentially composed -of granite can wade freely inthe subcrust or through ocean base, and where to, find an adequate force-to drivethe continents- against the resisting strength of the rocks involved. - Lowering ofstrength due to the rise of temperature in depths is to some exten,t compensated

Lee:Reflections w Twenty Years' Experience 37

by pressure. In the deep interior strength may conceivably deteriorate, though

rigidity may persist or increase. This, however, does not affect the surface rockwith which we are concerned.

High mountains being lifted 1gainst gravity are held by Jeifreys as stum-bling blocks in any line of argument conducive to the drift of continents, for

here again no known force is adequate to perform the work other than gravityitself. The paths opened by Joly and further explored by Holmes in tracing theorigin of the surface features of the earth indicate a bright and attractive approach.Rising of temperature below the surface through accumulated radio.active heatwould largely overcome the difficulty connected with rock-strength. The scenthowever darkens when we come to question our knowledge as regards the distribu-tion of radio-active substances not only in the interior of the earth but even onthe surface, and when Jeifreys points out that the adiabatic lapse rate in fusedrocks is not likely to be exceeded by their thermal gradient with the necessary

consequence that all convection currents have to come to a standstill. Few, ifany, loopholes can be found iii the abJe discussion contributed by Jeifreys onthese subjects once we admit the bases on which the arguments rest.

In his constructive effort this eminent geophysicist, like so many in theb_ophysical school, is however apt to simplify the geotectonic problems to thextent than is warranted by observational facts. A fracture inclined at 300 tOE

the earth's surface with a horizontal displacement of o km. and vertical displace-ment 40 km. is a picture that obviously does not depict the Large variety of.

geotectonic types known to the geologists. Nevertheless, Jeifreys ihdicated the wayin which the problem my be safely approached. Geological structure is the firstand last dictum provided by nature, that we cannot afford to stglect in any attemptto solve the problem of dynamic geology.

Starting from an analysis of the tectonic plan of this country I strived oirseveral occasions, to show how certain tectonic elements arrange themselves aftercertain patterns known as tectonic forms. The vast area of this country coveringa large part of a continent and bordering the largest and perhaps the oldest

ocean of the world provides abundant material and opportunities for such ananalysis. Traditional as well as the existing geographical boundaries in Europeare naturally liable to mutilate the views of the geologists on the general tectonic

plan of that part of the. continent. Moreover, marine transgression and deposi-

38 Bulletin of the Geologicezi Society of. China

tion in later geological ages, possibly accompanied by tension and regionalfragmentation in association with the development of the Atlantic have coverednd dislocated much of the tectonic traits of ancient times, and have given rise

to new systems of mountains in accordance pith the altered distribution of thecontinental mass. Here in this consolidated old latid no su.ch complex changestóok place in the later geological ages. Structural forms dating from ancienttimes iinfbid themselves: ii length 'and btcádth to our 'iew with traceablemodifications throughout' the successive orogenic epochs.

Taking advantage of these circuiustnces I have deilt elsewhere at somelength with the mote salient structural features of this country in three dominantgrous: the 'Cathaysian and neo-Çathaysian trends, the. former'. generally runningnorth-east, and the latter north-northeast, the east-w.est 'fo1d-zonc:and the variousshear forms The east west fold zis arose from a disturbance probably of deepseated nature, and have been subjected to north and south compressioit again andagain since Sinian ;times. The Cthaysían folds already. known to Punellyùnder the phraseology of'.the "Sinian system of fo'lding'? appèarto h 'ktgelr theresult of Palacooic movements, and the n.eo-Cathasiaií proba'bly..origitiated'fronithe latter part of the Mesozoic. Both of these types of folds includiug the moderngeosynclines, majT be interpreted as a consequence of a horizontal shear towards'he south, on the tart of the continental maas against tlze Pacific floor Thedominant shear form is that of the epsilon type,' numbering five or six, and eachextending over the whole or a part of a segment of the continent separated byth est-west zones. They 'often come to, interfere with the latter, and are some-times modified by, or adapted to, or even superposed on, teçtomc featutes belonging to other categories Thou mutual adiptation is also noticeable Detailedenquiry into the history of this type of tectoniL forms, e g , the Kwangsi ystern,has led to the conclusion that rudiments of it already existed in Palaeozoic times;and that it wa probably. brought to prominence by the Yenshan moyeutent. Inpassing I m.y say that fro.m field experience and laboratory experiments withplasto-elastic materials we. can no longer çntertain any doubt as to the .gciieral.arrangement of the component parts of 'this 'type of strucural pattern. The arcuate

. It has been proposee (Odell) that the epsilon type of shear-form would he nsore niitablyrepresented by the Greek letter ir Attention must however, he called to the possible misconcep-tion that the backbone of the system 'exteads beyond the frOntal are as that letter suggest.. Thefact is that the backbone alvsayi terminaths bcfre it teaches the frontal arc.

Lee :Reflec:ions on Twenty Years' Experience 39

front of the axes of the component folds and lines of thrust always faces' thesouth or south by west as observed in this part of the continent, with twó reikx.arcs of lesser dimension, one on each side, attached to the main frontal arc, anda backbone consisting of a longitudinal anticlinoriuin or a bundle of foldsstretching behind the frontal arc. If this description proves too broad to be. ofany practical value, attention might 'be called to the structural facts presentedbefore thi Society twO years ago inconnexion with a' discourse on the develo.pmen'of the structure' of the Kwangsi system.

The epsilon type or shear form as a strain figure disclosing the distoitionsuffered by parts of the surface ot the earth s crust is particularly illuinin4tmgfrom the point of view of dynamic geology It.is seen to have covered theEurasian continent with a grand sweep of the Eurasian arc and the backbone ofthe Urals already in paheozoic time Several 6f them are developed in westernEurope, though, there, the time relation between the component parts of each ofthe several system-s still requires a careful investigation Like the major part ofEurasia, the whole of the North American continent was essentially control cd bya tectonic framework of the same type in Palaeozoic times Instead of the prcsencof a bundle of compressed folds, like the Urals we have howcvei, in the American,system a broad longitudiQal up-arching formed in the rear f the main are,already recognized by A Keith ac the ' backbone of North America", and tosome extent revealed- in a number of the palaeogeographk maps of Ch. Schuchext.

All of these epsilon type of' shear-forms have their convex front facing the -equator. This can only mean one thing, namely, baek.in the: PalaeozQic'-.tinlesthe several parts of the continental surface in the Northern Hemisphere. coredby them were already sublected t3 a' horizontal .shearig oyemet, ''owrds theequator. The nature of the force engaged is then, clea,rly of a harmonic ;-thesecond order. The horizdntal component of th centrifugal fore aÑig ':trmthe spin of 'the earth, or more probably front ah-- increase of 'its rotatinãI speedis precisely' of that quality. On' the rçcognitiQn of' p1astoelastic pÓperties ofrocks- and frorn the ascertainment, of appreiabl variation' 6f the rotational speedof the earth within relatively shortperiods of-hioricalsixteenth to eighteenth centuries, 'it seems that geological past cans ;amply meet--the quantitative -requirement for the effective optration of that fote.

The distributiön -f the cast-west fold-zones is no less signifi'cant. Unlessthey are disturbed or over-shadowed b geosynclines and the horizontally sha'rcd

40 I3zul1eth of the Geological Society of China

masses, or hidden under younger sedimentary covers, we can always find them.in definite latitudinal positions. In the eastern Asiatic continent these zones havebeen identified in latitudes 57°-8°, 41°-42°, 330.340, and 25°-26° with aninterval of 8° separating each successive pair. Similar zones occur in westernEurope, North America and South Africa in corresponding positions, though varyin each case in the intensity of compression and the date of dominant folding.The apparent extension of the American zone into the Atlantic sea-board of

North America, the strange bending to a nearly eastwest trend suffered by theAppalachian Mountains in Pennsylvania, the existence of the Ouachita Mountainsand the occurrence of the group of islands to the south of the Santa BarbaraChannel together with the extensive east-west line of thrust in the Santa YnezMountains on the north irrespective of the presence of the formidable CordilleranRanges in the neighbourhood are facts which can hardly be explained unless wegrant the patent influence of the east-west zones. It will not be surprising ifsome day geologists will succeed in detecting an underlying tectonic cause belowthe surface rocks that form the borderland between Canadtand the United Statesin the upper reaches of the South Saskatchewan River on the one side and of.the Missouri on the other.

Natural sceptism among geologists and geophysicists may . redicule thisregularity in the distribution of .the east-west zones as of significance any morethan the so-called Bode's law in defining the spacing of the planets. Nor havewe any reason, as yet, to compare this zonal structure of our continents withthose observed znes in Jupiter and Saturn, for the latter are apparently cpmposedof gaseous material and rotating in the different zones of the same planet with aconsiderable difference in velocity. Nevertheless fthtures that attain such a widedistribution over the visible part of the surface of the earth's crust and play suchan important rtle in tontrolling the tectonic plan of. the regions. that are notdislodged by sheared masses cannot be disposed of light-heartedly. In his analysisof gravitational potential G H. Darwin already showed certain critical strainsurfaces cropping out on the face of the earth in zonal arrangement parallel t

the -equator. His theoretical deduction as to the latitudinal position of the zonesdoes not of course agree with the observed facts. Whether we can arrive at anagreement by adjusting the initial assumptions is a matter for the geophysicistto decide. At all events the nature of the operating force scms to. accord,witha zonal harmonic of some high Order.

Lce:Reflections on Twenty Years' Experience 41

For the moment it seems satisfactory to account for the vast sheared sheeton the continents and the backward sliding against, the direction of rotation of

the' earth on the part of the American continents by attributing plasto.elasticproperties to rocks and by postulating periodic outbursts of stored stresses arisingfrom a continual increase of the earth's rotational speed.

The centrifugal force as a potent agency that directs river erosion is a well-known, but sometimes neglected, fact. As early as in r86o Baer called attentionto the strange phenomenon that all the meridionally flowing rivers in Russia cutsteep banks on the right-hand side. Likewise, you will find the mighty Yangtzeunder-cutting steep cliffs on the right-hand side as soon as it leaves the gorges...

There is a definite constraining force operating on the flowing material in a direc-tion perpendicular to the flow, and that force is associated with the rotation ofthe earth. This commonplace is known to every physicist; but I am not sure ifevery physiographer has paid due attention to this importantfaçt. I have referredto this matter not only because of its importance in determining the behavioürof large rivers, but it makes the to realize how negligence of unfamiliar findingsmight bar scientific progress. This brings me to a subject closely connected withour physiographical research.

some of us will probably remember that twenty years ago when this Societyheld its first meeting number of scratched boulders were exhibited in the odd-corner of the room, and that it was suggested that they might possibly be ofglacial origin. The unfortunate. specimens met a cold reception: For morethan ten years. hence the evidence wrought out from the North rather tended todiscredit any such untoward occurrence. Geologists working in the field,. includ-ing myself, felt shy to turn their eyes any more on such queer boulders. A(ter.

working for two successive summer sessions in the Lushan I was however struck.by certain erosional features which I failed tó explain away by the activities ofrain and stream. They haûated me, I may say, for two years. Yet, thçy remainedunexplained. It was not until the forgotten boulders found in the North downedon me that I began 'to gather thoughts on the possibility of glaciation. Subsequentinvestigation disclosçd some amusing mistakes which I made in the early stage ofstudy as regards the arrangement of moraines around the Lushan, but the evidencefor a local glaciation accumulated as fieldwork proceeded. The finding in the-

Huangshan of remarkably well-preserved glacial markings n an abraded surface ofthe Huangshan granite which forms one side of a. morè or less demolished U-valley

42 Bulkin of Me Geological vcie1y of C/iia

rendered .evjdence for glaciation final and absolute. Mote substantial supportwas soon available from the shore of the Poyng Lake. When it is recalled thatabout a century ago how Agassiz aroused the anger öf von Buch by the enuncia-tion of his theory on the vanished glaciers in the Upper Rhone valley, I rnunrejoice over the happy atmosphere in which our work could have been carried on.

Further advancement in glaciology has given rise to numerous problemshitherto passed unnoticed or even miss-treated. lt seems desirable, at the presentstage of ehquiry, to map out, as far as w. can, the extent of glaciationfor eachglacial period, and to ascertain the intervals covered by the interglacial in areaswhere th presérvd evidence admits suh undertakings. Information so faraccesible to me ïéarding these qûcstions leave littl doubt that we have to dealwith: polygracíatioÎa, and 1with nuaierous high-lying área cbvered by independentlocal ice-caps which, at one tiúje 6r anöther, séit out tongues of ice to the Íowlaiidin the xieighbourhoode

A typical example is afforded by the. Lushan in the central Yangtze valley.The highest part in the glaciated northern half of this mountain rises to a heightof 1,480 m. above the sea level, and the bottom of the firn basins is on the averageabout 480 m. lower. There are altogether seven basins of moderate size, eachof which nourished a neye, and supplied ice that descended to the surroundinglowland The largest of these basins is situated an the ntith eastern part witha fairly well preserved cirque hanging on its southera side and an extensl%e sheetof moraine spreading over the foothills and the north eastern plain A series ofarcuately arranged end moraines were recognized, the faíthest of them statids onthe shore ot the Poyang Lake, separated from the foot of the mountain by adistance of about 9 km Olose examination showed the existence of two differenttypes o moraine: the one is dark red in colour, mottled, considerably hardenedand appxeciably laterized, and th other brilliantly red in colour also mottled,loosely aggregated and occasionally showing incipient laterizat!on The hardenedtype is sometimes overlain by gravels, which in turn bya darkred loam likewisehaidened and notabty laterized.

Although no exposure has yet been found that discloses. thè superpositionof *he Ioos type in relation; to the hardèxiedmorihe, lenticular banks: 6f thelatter wer 'observedthat weréinvólved iû Uic loosé.rnoràiné: Sharp distinctionbetween the 'tWo ecludes-all possibiliti thi:hardeúih and-laerizátion could

L,ee:'Rcflec:ions on Tw.nty Yeais' Experience dB

have proceeded from the core of a heap of the loose moraine after its dcpositin.We are thus led to conclude that two glaciations took place in the surroundingplain of the Lushan separated by aiïiiiterglacial periád sufficiently long and witha sufficiently hot and humid climate as to be able to effect the latcrjzation ofthe older moraine. A third type of moraine, brown in colour, unassociated withthe red clay, without any trace of mottling or the slightest sign of laterizationonly occurs i the higher part of the mountaxnaboe the altitude of 800 to 900in That this difference in composition cannot be attributed to the difference

in height of the places where it ociurs is shown by the fact that pockets of oldermoraine with precisely the same characterisucs ns observed in the lowland arestill to be seeiion sheltered spots in thè hhèr at of the iiiounain. To theLushan area we have then altogether three glaciations. Naming in the order oftheir aniquity they are the Poying, the Taku and the ushaa glacitiôns; withthe prbability that Taku. is to be separated into two stadia. This, hpwever, isnot the place for a detailed discussion.

Anothe locality that offers opportunities for thestûd' óf polyglaçiatiónhappened to be noticed when I journeyed sn western I-Iu\eh This is the Enshihdistrict The evidence gathered here is of a different kind, and may serve to

illustrate another promising approach In the western part f the elongated,mounta n locIed basm of Enshih boulder clay is widespread on both sides of theChingkia ng River forming a large nui1er of dtumlis with, and sornetimeswitliöut,a nucleus of bed rock Throughout the moraine coered country the generaltopography is wonderfully smooth even in places where the young red sandstone,usually of cliff-forming habit elsewhere, is exposed on the surface. Whereâs inthe eastern part. of the basin, namely, cast of the Iinè drawn fro the villageKintzepa. a drastic change n topogrpy suddenly takes plac, but the bed-rockis still the.yoig red sandstpne. The rolinghi1lspbserved to the west of thatline no longer ex.ist. to the est of i;,, InsteçJ the. whole. aiea of that part ofthe basin is çiverrun by a labyrinth of gullçys ad:. abandoicd stream .çouseswhich travel in, all conceivable directions.between .numçröus. pyapis formed ly.the young red sandstone. As viewed from a distance, the 4isecte sandstonepresents an appearance that almost rccallsbad land. The remarkable fact is thaton the pyramid hills occasionally occur erratic boulders of distant origin.

it is thus probable that a glaciariôn 'toôk paét in a xoi remOte pastbeing féllowed by lng intetval f tieath râidr :rith The resulting heavy

44 BoJiein of tue Geological Sociely of China

incision of the land and a general sweep of the moraine except a few scattered-boilders. Then carne the glacier that moulded the soft landscape in the westernpart of the basin and left abundant moraine. For a distance of about 4 km. theChingkiang follows a singularly straight course as soon as it descends to the basin.on both sides of thepresent river:bed stands a perfectly smooth, straight andnioderately inclined- rocky wall which abruptly disappears at a point where theriver turns to the south-east. It seems apparent that for this length the riverbed was once occupied by a small glacier which, judging from the freshness ofthe erosional features that it left and their discontinuity with the -far more advancederosional landforms in the lower part of the valley, cannot be the last remnantof, the continually retreating glacier that deposited the extensive sheet of morainein the western part of the -basin. In other words, these features probably representa third, though diminished glaciation.

These deductions are in fact supported by the development of moreerosional features observed higher up ¡n the mountáins. On -the eastern wall ofan elevated valley extending between Maotien and Changliangtze, - about halfway between Patung and Enshih, three terraces are successively developed. Onclose inspection it turns out that each of these terraces does not consist of a.platform with the ¿isual flat surface, but assumes the form of a trough with its -

axis following the general strike of the valley. The rocky walls on both sidesof the trough are exceedingly smooth and straight, and form a U-shaped curve-in cross-section. Each of them undoubtedly represents a part' of a glaciatedvalley in the past, but has had its western wall largely removed soon after thedisappearance of the glacier, for in all the troughs striated boulders were found.

The original source of the striated boulders is illuminating. The mainvalley and the overhanging troughs on the side-wall are all carved out of aregular succession of. strata ranging -iñ age - from the Lower Carboniferous tóLower Triassic and dipping uniformly to south of east at an angle of 25° to30°. By restoring the demolished valley-wallsthrough extrapolating the U-shapedeurve for each trough we can readily find out the' kind of rocks that.forrned thevanished walls on the western side. Thus we àrè enabled to see in the restored'walls that certain rocks stood high above the bottom of a trough whçn it wasin -a complete-U-shape, but at present those rocks are only exposed below thebottom of the trough. Now the fact is that among the sxriated boulders foundin a particular trough there occur numerous specimens of rocks that are actually,

Lec:Reflections on Twenty Years Experience

nly exposed below the bottom of that trough. Topographical as well as tectonicconditions of the area arid the shape of the striated boulders forbid the assumptionthat they could have been brought over fröm distant sources.

These circumstances lead to the conclusion that when the uppermostU-valley was formed its position was considerably higher than the present valley.Since the lower part of the valley was under the protection, or was subject to auniform erosion, of the glacier, the melting water took the advantage of a lateraldrainage,an important fact to be noticed in connexion with the drainage habitof most of the mountain glaciers existing to-day---aud cut a channel which mayeven reach a level lower than the bottom of the valley. When the glacier wason its growth, such a channel would be blocked; but when it was on the retreat1or finally to disappear, then it was that channel, but not the valley-bottom,that bore the blunt of the torrents. Eventually a gully or trench was formed;and enlarged, and might develop a sharp V-shaped valley provided that themountain-strearn was allowed to perform its destructive work for a reasonable

length of time. The new V-shaped valley thus formed below the originalU-valley would serve as the site for the invasion of the next glacier which, intime would transform the V-valley to a U-valley with consequent destruction ofone of the walls of the original U-valley.

Thus from an alternation of glacial and interglacial periods there is nodifficulty to see why the Uvalley shifted, stage by stage, to the west and at thesame time lowered itself doîn step by step. The first and second troughs areseparated by a vertical distance of nô in., the second and the third by 40 m.,and the third stands some. 40 in., higher. than the present valley-bottom. At

the bottomof the present valleyis ah exposed surface ofthe Wutungsandstone,an exceedingly hard, quartzitic sandstone, bears numerous glacial strialions inthe neighoúrhoód of Little Maotien This represents the last glaciation. Traces

of this last glaciation however disappear lower down the valley of Santaoyen, aplace which stands at an altitude of about i,aoo m. above the sea level incontrast with the fact that the sculptured landforms and moraines due to theolder glaciations petsisted to the Chenshih and Enshih basins. The altitude ofthesc bains is estimated at 540-780 m. above the sea level.

The result arrived at from the developthent of iandform.s in the vicinityof Maotiesi is therefore in complete agreement with the evidence afforded by the

46 Bulletin of tile Geological Society of Cilinu

Eashih Basin as regards the extent of the three earlier glaciations. These, inturn, may be: compared with the. three glaciations observed in the Lushan area.The fourth which was confined to mountainous regions higher than. 1,200 m.was naturally absent from the Lushan area. From the general lowering ofsnow-line in the successive &laciai periods. H y. Wissmann deduced that theobserved glaciation in the Tientsangshan, Yunnan, could not be compared inpoint. of time, with any of glaciations of the Lushan area, but that the Tientsang-shan, or Tau glaciation represented the last glacial period iii China implyingits:equivalency to the Wurm of Europe.

The question as to how far the three earlier glaciations extended to thesouth, is one thât cannot be answered with safety at present. We know howeverthat the high mountains in eastern Kwangsi . and southwestern Hunari even.including the Kupqshan were once or twice glaciated. East of the Kuposhan theline demarking the glaciated and unglaciated areas appears to recede sharply to thenorth, passing probably the high mountains of central Kiangsi, those of southernAnhwei and then finallystriking the Tientai and .Yentang in .Chekiang. West.

of the Kuposhan the line of demarkation also recedes to the north It xtends

north-westward, past the southern part of the Kongcheng district, crossing thenorthern part of the Yaoshan and then, entering into the bordering districts.between Kweichow and Kw'angsi. It should be reiterated that north of. this linewe may expect the occurrence of local ice-caps, but by no. means are to dealwith ice-sheets of continental scale.. . The question with the Kweichovv plateaustill .rêmains puzzling.. Trades of individut glaciers have been found on itsnorthern, eastern and southern sides. No positive evidence is however yetavailable showing that the whok plateau was once buried under a vast ice-cap.Only a number of iädpendànt básias on this plateau arc marked by the. presenceo moràines. and .fluvio-glacial.dáposi'ts. Whether this;state of. affairs is due to..post-glacial erosion or. to the existence of rn basihs .cöntinued to 'areas

covered by the moraine is. a quèrtion that remains to be sólved.

Numerous other points connected with other branches or geological researchin this count:y might be submttted for your consideration on this occasion Irwould be, however, too pretentious and certainly impossible fot me to coverthem all. Before concluding I presume that you would join me to pay ourhomage to those pioneers, who;.for the' sake of genuine scientific interest,svOrkcd here, .under.,dilllcult . conditions in the early day.s,. and left.' us with.

Lee:Refleciions on Twenty Years' Experience 47

monuientary contributions which served as corncrstones for further research,and also that you will join mc in expressing our gratitude to the GeologicalSurvey of China for its continual support, and, iñdeed, nursing of this Society inthe past twenty years. Now, it is time, according to the world-wide custom, theyouth has to be prepared to stand on his own feet. And we may be assured this daythat this young organization bids fair to prove its worthiness in the great future.