180 Charles Maclaren, Esq., on Grooved and Striated Rocks 



distances ; here, however, part of the effect may be due to 

 glaciers. 2. Travelled masses of trap and other enduring 

 rocks in the basin of the Forth, carried eastward from their 

 parent rock in great numbers, and chiefly for short distances. 

 3. Numerous blocks of the greenstone of Salisbury Crag, torn 

 from the top of the precipice, and carried eastward, most of 

 them only for a space of one or two furlongs, but some trans- 

 ported across the ravine, and lodged on Arthur Seat. On the 

 same principle, the removal of the multitude of angular blocks 

 of porphyritic basalt, resting on the skirts of the south-east 

 limb of Arthur Seat, and evidently torn from the upper part 

 of that limb, may be accounted for. 



Rarity of ancient moraines. — I looked in the grooved valleys 

 of the Grampians for remnants of ancient lateral moraines, 

 but saw nothing that could be considered as such, except in 

 one instance at Gareloch. Perhaps their disappearance may 

 be referred to certain geological changes, of which, in the 

 opinion of Agassiz, and some American geologists, distinct 

 traces exist. They think that at the close of the glacial 

 epoch the sea rose and covered the mountains of the northern 

 parts of Europe and America to a great height, and then 

 again subsided and left the land dry as before, though not 

 perhaps at the same level. During the rise and fall of the 

 water, deposits of moveable matter, like these moraines, must 

 have been very often remodelled or swept away. We have 

 evidence in support of the alleged changes of relative level 

 in the fact that strise and grooving, certainly produced by 

 glaciers on terra finna, are found covered by the old boul- 

 der clay, which has been deposited from water, and which 

 ascends to the height of 800 feet at least above the present 

 seas. 



A similar inference may be drawn from facts whicli the beds 

 of our rivers present, and which indicate three successive 

 conditions. First, the bed was a channel cut on the dry land 

 by the stream; next, the land was submerged, and the channel 

 was filled up by the boulder clay ; thirdly, the land rose 

 again above the sea, when the river began to resume pos- 

 session of its old channel, or in some instances, perhaps, 

 formed a new one. I refer, as an example of these changes, 

 to a section on the River Allan near Stirling. 



