10 GSA TODAY, May 1998

The greatest petrologist of the 20thcentury is clearly Norman LeviBowen (1887–1956). He promotedthe solution of petrological field

problems by the application of principlesdeduced from simple phase diagrams of theend members of common rock-formingminerals, thereby providing a quantitativeapproach to a field previously concernedonly with observation and classification.Despite his quiet personality, subdued pre-sentations, droll sense of humor, and evenhis small stature, he was a giant.

Work and PlayAs a youth, Bowen helped his father in

the family bakery, driving the delivery rig—an experience that resulted in his enduringdistrust of horses. Winters were spent iceskating, and during the summer months hebecame a strong breast-stroke swimmer andtook part in races. He sang in the choir ofthe local Anglican church and is alleged tohave had a fine tenor voice.

The Field ExperiencePublic schools in

Kingston, Ontario, had pre-pared him for college entranceexaminations at Queen’s Uni-versity. Even though registeredin the arts course with theintent of becoming a teacher,Bowen had the urge, as manyyoung people do, to see newand alluring country and toearn some money. He joinedan Ontario Bureau of Minesgeological mapping party toLarder Lake under the leader-ship of R. W. Brock. Brock,who was an outstanding per-sonality and eventuallybecame Director of the Geo-logical Survey of Canada,had so much confidence inBowen’s inherent abilities, inaddition to his skills for sur-viving in the bush, that he leftthe young man to carry outthe work alone! Travel in thebush was by canoe, andtraversing in search of out-

crops was done under a blanket of mosquitoesand black flies. Bowen could use an axe andtump line, make pace-and-compass surveys,and cook. In the course of his mapping, hebecame interested in the differentiation ofdiabase.

Courses ChosenAs a result of his field experiences,

when he returned to Queen’s University,Bowen registered in the School of Mining,taking mineralogy and geology. After twomore field seasons around Lake Abitibi andGowganda Lake, again paying attention tothe diabases, he won a prize of $25 and thePresident’s gold medal from the CanadianMining Institute for the best paper submit-ted by a student: “Diabase and aplite of thecobalt-silver area.” (See 1956 edition ofBowen [1928] for references to his pub-lished works.) Trained in the Canadianbush on the myriad of variables in naturalgeological processes, he had rapidlyabsorbed the principles of geology and

chemistry. On graduation in1909, he won a London Exhi-bition of 1851 Scholarship,which gave him the opportu-nity to continue on in gradu-ate school.

Charismatic TeachersHe was first attracted to

Norway because of J. H. L.Vogt’s (1903–1904) book, DieSilikatschmelzlösungen and byW. C. Brøgger, who hadapplied physicochemical prin-ciples developed in the inves-tigation of slags to the prob-lem of differentiation. Bowenwas discouraged, however,from going to Norway becauseof the language barrier andbecause Brøgger was too busywith legislative duties. Instead,Bowen went to MIT to studyunder the sparkling andcharismatic teacher ReginaldA. Daly, who indoctrinatedhim with the idea that basalticliquid was a primary magmaand all others were derivative.

He also introduced Bowen to some of thepossible causes of differentiation, such as dif-fusion, fractional crystallization, crystal seg-regation, gaseous transfer, immiscibility(liquation), and assimilation. ProbablyCharles H. Warren imbued Bowen with theprinciples of physical chemistry as applied to mineralogical and petrological problems.It was clear that he had already focused onigneous differentiation and the principles of physical chemistry.

The Experimental ExperienceIn 1910, at the suggestion of T. A. Jag-

gar, then at MIT, Bowen applied to the Geo-physical Laboratory at the Carnegie Institu-tion of Washington to do an experimentalstudy related to a geological field problemfor partial fulfillment of the requirements ofthe Ph.D. As the laboratory’s first predoc-toral Fellow, he was assigned the “nepheliteproblem,” a favorite topic of J. P. Iddings. Atthat time, most of the experimental tech-niques for high temperatures used todaywere all in their early stages of develop-ment. The controllers for the high-tempera-ture furnaces were very large street-car-typebanks of resistor coils; platinum-rhodiumthermocouples had just been calibrated to1755 °C by Day and Sosman (1911); thequenching method had just been inventedby Shepherd, Rankin, and Wright (1909).Wright (1910) had perfected a new petro-graphic microscope for examining fine-grained synthetic preparations. Particularlyimportant was the development of a calcu-lation scheme for translating the chemicalanalyses of rocks, whether crystalline orglassy, into a set of end-member minerals,the CIPW normative system (Cross et al.,1902), that could be simplified for labora-tory experimentation. In addition, the the-ory of solid solutions had been laid out byH. W. Bakhuis Roozeboom (1901). In short,Bowen arrived at a most opportune time to do the nepheline-anorthite system—allthe tools and theory were in hand. Thenepheline-anorthite diagram was deter-mined with considerable efficiency with 17different mixtures and 55 quenching experi-ments under the tutelage of E. S. Shepherdand F. E. Wright. That simple system, thefirst example found in silicates of solid solu-

Norman L. Bowen: TheExperimental Approachto PetrologyH. S. Yoder, Jr., Geophysical Laboratory, Carnegie Institutionof Washington, Washington, DC 20015, yoder@gl.ciw.edu

Norman L. Bowen on hisfirst job involving landsurveying.

Thecourtshipof N. L.Bowenand MaryLamont, amedicalstudent inBoston.

GSA TODAY, May 1998 11

tion combined with polymorphism, gener-ated in Bowen’s mind a much larger picture.While writing his thesis he also managed toproduce in 1912 a paper of lasting value,“The order of crystallization in igneousrocks.” With this publication at age 25,Bowen had introduced the precursor to amajor change in the approach to petrology.

Career DecisionIn the summer of 1911 Bowen was in

the field again with Reginald Daly, surveyingthe Shuswap terrane of British Columbia,famous for its crosscutting granites andwholesale injection. In spite of his absencesfrom Boston, he managed to court MaryLamont, and they were married on October3, 1911. Upon graduation from MIT on June4, 1912, he had offers from Jaggar, then atthe Volcano Observatory in Hawaii, for apost in economic geology at Tucson, for aposition at the Geological Survey of Canada,and for the job of assistant petrologist at theGeophysical Laboratory. After another fieldseason in British Columbia, in charge of hisown field party, he decided to join theGeophysical Laboratory staff, arrivingSeptember 1, 1912 (Yoder, 1992).

Critical Mineral SystemsPlagioclase is the most abundant mineral inEarth’s crust, so Bowen next undertook astudy of the two-component system albite-anorthite. That system, studied earlier byDay, Allen, and Iddings (1905), was thesubject of the first official publication ofthe Geophysical Laboratory. They had beenable to determine the melting temperatureonly from An100 to An26.1 Ab73.9. Kineticproblems prohibited their measuring thesolidus temperature with the cooling-curve

method, even though they recognized thesystem as one of the Roozeboom theoreti-cally possible types, with continuous solidsolution containing neither a maximumnor minimum. With the quenchingmethod and run times of only 1/2–2 hours,Bowen was able to generate the entire pla-gioclase diagram, well documented withlater studies. It provided the basis for hissubsequent views on magma differentiationand crystal fractionation, both old ideas(Scrope, 1825; Becker, 1897) but lackingexperimental demonstration.

A New Integrated ApproachSeveral alternatives for the processes

leading to magma diversity had alreadybeen presented and explicitly summarizedby Iddings (1892). But Bowen set out hisprejudices forcefully and clearly in 1915 intwo papers after studying only two more,yet most critical, phase diagrams illustrat-ing the reaction principle. One paper, “Thelater stages of the evolution of igneousrocks,” provided a flexible, broad theorybased on quantitative experimental obser-vations that he defended with rigorousargumentation. As a result of his incredibleperceptiveness and intuition, Bowen hadintegrated all the new experimental meth-ods, physicochemical theory, and fieldobservations into a unified new approachto petrology. It was his clarity of presenta-tion, documentation of principles withexperimental demonstrations, and applica-tion to specific field problems that eventu-ally made his 1928 book The Evolution of theIgneous Rocks, the handbook for petrologistsworldwide. It was with some reluctancethat field geologists eventually acceptedBowen’s philosophy as leading to the mostsatisfactory interpretation of the facts asthey were perceived by geologists: (1) recog-nition of a set of field observations thatappear to be related; (2) simplification ofthese relations into a set of laboratoryexperiments analogous to the conditionsbelieved to have existed in nature; (3) exe-cution of those experiments in an unam-biguous manner; (4) application of theprinciples derived from the experimentalresults to specific field occurrences; (5) re-examination of the field relations and test-ing the new principles with additionalobservations; and (6) reiteration of the

above sequence until a satisfactory solutionis achieved, recognizing that any newobservation or inconsistency may initiatethe process again.

Successful PhilosophyAfter half a century, it is clear that his

philosophy had been successful eventhough new interpretations of the detailswere required (Yoder, 1979). Bowen’slegacy, in addition to the many accurateand precise phase diagrams of the endmembers of common rock-forming miner-als, is the construction of an experimentaland theoretical basis for the interpretationand documentation of the diversity ofigneous and metamorphic rocks.

References CitedBecker, G. F., 1897, Fractional crystallization of rocks:American Journal of Science, ser. 4, p. 257–261.

Bowen, N. L., 1928, The evolution of the igneous rocks:Princeton, New Jersey, Princeton University Press,334 p.; second edition, 1956, New York, Dover.

Cross, C. W., Iddings, J. P., Pirsson, L. V., and Washing-ton, H. S., 1902, A quantitative chemico-mineralogicalclassification and nomenclature of igneous rocks: Jour-nal of Geology, v. 10, p. 555–690.

Day, A. L., and Sosman, R. B., 1911, High temperaturegas thermometry: Carnegie Institution of WashingtonPublication 157, 129 p.

Day, A. L., Allen, E. T., and Iddings, J. P,. 1905, The iso-morphism and thermal properties of the feldspars:Carnegie Institution of Washington Publication 31, 95 p.

Iddings, J. P., 1892, The origin of igneous rocks: Philo-sophical Society of Washington Bulletin, v. 12,p. 89–213.

Roozeboom, H. W. Bakhuis, 1901, Die HeterogenenGleichgewichte vom Standpunkte der Phasenlehre:Braunschweig, Germany, Friedrich Vieweg und Sohn,Vol. I—221 p.; Vol. II, 3 parts—467 p. (1904); 226 p.(1918); 199 p. (1918); Vol. III, 2 parts—313 p. (1911);348 p. (1913).

Scrope, G. P., 1825, Consideration on volcanoes: Lon-don, W. Phillips, 270 p.

Shepherd, E. S., Rankin, G. A., and Wright, F. F., 1909,The binary system of alumina with silica, lime andmagnesia: American Journal of Science, ser. 4, v. 28,p. 293–333.

Vogt, J. H. L., 1903–1904, Die Silikatschmelzlösungenmit besonderer Rucksicht auf die mineralbildung unddie Schmelzpunkt-Erniedrigung: Christiana, Norway,Jacob Dybwad, 235 p.

Wright, F. E., 1910, A new petrographic microscope:American Journal of Science, ser. 4, v. 29, p. 407–414.

Yoder, H. S., Jr., 1979, The evolution of the igneousrocks: Fiftieth anniversary perspectives: Princeton, NewJersey, Princeton University Press, 588 p.

Yoder, H. S., Jr., 1992, Norman L. Bowen (1887–1956),MIT class of 1912, First predoctoral Fellow of the Geo-physical laboratory: Earth Sciences History, v. 11,p. 45–55. ■

The plagioclase phase diagram, with temperaturein °C and the seven new synthetic and two naturalanorthite-albite compositions studied, indicatingthe liquidus (upper curve) and solidus. The melt-ing point of anorthite was already well establishedand used as a point for thermocouple calibration.

Walcott Biography To Be PublishedGSA original Fellow and 13th president Charles Doolittle Walcott is the subject of a biographyby Ellis L. Yochelson; it will be published in June. Yochelson’s Rock Star profile of Walcott, afamous paleobiologist and biostratigrapher, was in the January 1996 issue of GSA Today. Thebook covers Walcott’s life from birth in 1850 until 1907, when he resigned as third director ofthe U.S. Geological Survey to become secretary of the Smithsonian Institution.

The book is available from Kent State University Press, P.O. Box 5190, Kent, OH 44242(not available through GSA Publication Sales). Charles Doolittle Walcott, Paleontologist isavailable at the prepublication price of $40, including postage and handling, for a limitedtime (after July 31, 1998, the price will be $53). All orders must include payment and thetitle of the book; Ohio residents add 6.25% sales tax.