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182 LOCH LONG AND LOCH LOMOND.
canyons and other phenomena connected with streamerosion.
REFERENCES.Geo!. Surv, Map, Sheet 31.1909· TYRRELL.-No. 3,1912, 1914. MACNAIR and CONNACHER.
VIlI.-LOCH LONG AND LOCH LOMOND.
By J. W. GREGORY, D.Sc., F.R.S., F.G.S.
The West Highland railway follows the Clyde valley to Dumbarton, passes its conspicuous volcanic neck, then crosses theUpper Old Red Sandstones. West of Dumbarton the railway traverses a raised beach, which ends at the foot of a line of cliffs, tothe north of the line. From Craigendoran the railway ascends overOld Red Sandstone till it crosses the Highland Boundary Fault.The first of the older rocks are the greywackes at Row Station,which are followed by slates, with a basal quartz conglomerate.At the head of the Gareloch the line passes from smoothweathering albite schists (exposed e.g. on the slopes of Strone Hillto the east) to a band of crumpled schistose grits, which have a veryrugged aspect at Whistlefield, as the rocks have been induratedand quartz-seamed along ancient fractures. The line thenreaches Loch Long, one of the best fiords in south-westernScotland. Owing to its long, straight course it is used as thetorpedo range.
Hanging valleys are seen on both sides of the loch. Afterpassing Glen Douglas the view across the loch to Glen Croeshows one of the numerous pre-glacial river valleys of this districtwhich retain their river-cut features. Glen Croe is a narrowsinuous valley with overlapping profiles. The spur which formsthe left bank at the mouth of Glen Croe is smooth and glaciatedto its end. The features seen in this passing view indicate thatGlen Croe has been but slightly modified by ice action, that thevalley had been cut to its present depth in pre-glacial times, andtherefore that Loch Long had then been cut down at least to sealevel. From Loch Long the railway passes to Loch Lomondthrough the windgap at Tarbet, the former course of the CroeWater.
The banks of Loch Lomond are best seen from the steamer.The voyage down the loch gives the opportunity of observingthe moraines at its northern end, the steep eastern face, the hanging valleys as at Inversnaid, the Highland Boundary Fault, and thetilted Old Red Sandstone conglomerates beside it. This sectionled Nicol (1863) to the view that the rocks in this district occurin a descending series from south to north. At the southern endof the lake are good views of the northern face of the lavaplateaus and of many conspicuous volcanic necks.
