Glaciers in Scotland in Ancient Times. 33 



larly over the surface. They are most numerous at or near 

 the beach, as may be seen on the west side of the loch, where, 

 from the absence of buildings, few have been used up. On 

 the highest part of the hill c, they ascend to about 800 feet 

 of elevation. Above that height there are scarcely any visi- 

 ble ; but some may have been broken up for fences. The 

 summit of the ridge ^, seems also nearly bare of boulders. 



The granite boulders, which are all much rounded, could 

 not come from any spot nearer than Ben Cruachen, 30 miles 

 northward. Those of greenstone are generally deprived of 

 their angles, and must have travelled some miles, since that 

 rock, though existing in veins a few miles northward, no- 

 where appears in situ on the shores or sides of the loch. The 

 mica-slate blocks, also, must have been brought to the places 

 where they rest by some agent, for, except at a few points 

 on the beach, there are no precipices from which they could 

 roll down. Moreover, we find blocks of the proper mica- slate 

 resting on the strata of quartzose chloritic rock with which 

 it alternates ; blocks of the latter resting on strata of the for- 

 mer ; and at Row, blocks of both resting on the clay-slate. 

 All these facts prove that the boulders have been moved, and 

 that their motion was from north to south. 



Now, let us suppose a glacier, having its source in the 

 mountains beyond Loch Long and Loch Goyle (M and Y in 

 fig. 5), to occupy the valley of Gareloch, its motion would 

 be southward ; it would transport the largest masses we have 

 described in that direction; if it diminished gradually, it would 

 leave a succession of terraces (moraines) like 1, 2, 3, 4, and 

 scatter blocks over the surface ; by friction on its bed, it 

 would form a slimy clay, such as we find coating the beach 

 and declivities ; it would deposit a bank of moveable matter 

 at its lower end, like the point at Row ; finally, it would 

 abrade, smooth, and round off the rocks, and leave scratches 

 and groovings on their surface,^running parallel to the axis of 

 the valley, precisely such as we see at Gareloch. We have, 

 then, not merely a few, but all the distinctive marks of gla- 

 cier action at Gareloch, forming in the aggregate a body of 

 evidence which seems to me to exclude the supposition of 

 any other agency. 



VOL. XLII. NO. LXXXIIL— JANUARY 1847. C 



