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PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 25, 



up the river. The shell-bed here is very similar to the one already- 

 described : it is a dark-coloured, compact clay, with small stones 

 and the same species of shells. Over it is a sandy bed, 12 to 15 

 inches thick, and above this an Upper Drift of earth and stones. A 

 small part only of the section is vertical ; the largest part, up the 

 river, is broken and tossed, and covered with wild shrubs. An 

 observer who had not previously studied the Clenid Burn section 

 would be very likely to confound the sheU-bed here with the Boulder- 

 clay. 



On the east bank of the Crook-Crever Burn, a tributary of the 

 Slaodridh, about one mile north-Avest of Lag, fine sections of these 

 beds are seen. The one I shall first notice is at the upper end of a 

 long and deep gorge which the river has cut out in soft sandstone 

 and shale. Sandstone-rock is the base of the section ; over this is a 

 bed of Boulder-clay, 30 or 40 feet thick, the clay being hard, com- 

 pact, and of a structure almost unworkable, with fine examples of 

 striated stones, both blocks and of smaU size. Its upper part for the 

 thickness of a foot is a hard, dark- coloured, gravelly sand or sandy 

 gravel, extremely hard and obdurate under the pickaxe. Over this, 

 and strongly contrasted with it, lies the shell-bed : it has a structure 

 very similar to that already described. The clay is dark and com- 

 pact, but very diff'erent from the Boulder-clay below in the compa- 

 rative facility of working it ; there are a few small stones, rarely 

 striated. Besides the shells already named, a perfect Leda was here 

 met with, and fragments of a Balanus. Above the shell-bed are 

 Upper Drifts, like those already described, and strongly contrast- 

 ing with the true Boulder-clay at the bottom of the section. 



Fig. 1. — Section of tJie Drift-beds of Arran. 



Croolc-Crever Burn, 



a. Boulder-clay. 



b. Shell-bed ; Arctic species. 



c, d. Upper Drifts. 



s. Sandstone and shale. 



Another very good section is met with further down the stream, 

 a little way below the sandstone-gorge above referred to. The bed 

 and banks of the stream are here formed of soft shale, dipping S. W., 

 and rising high on the east side. Over this the Lower Till and other 

 beds are laid in the usual order, following the inclination of the shale, 

 and apparently thinning out westwards. The wash or facing and 

 the debris having been cleared away, the entire section was laid open, 

 from the underlying shale to the Upper Drift-bed ; and nothing could 

 be more interesting or perfectly satisfactoiy than to notice the con- 



