200 Charles Maclaren, on 



eight), but the parallelism of their striation was perfect, and 

 I was surprised and mortified to find, that when I examined 

 the district, and published my account of the striated rocks of 

 Gareloch, three or four years previously (Edin. Phil. Journal, 

 Jan. 1846 and Jan. 1847), the parallel striation of the boulders 

 had been entirely overlooked. It was Mr Smith's observations 

 at Row, that brought me back to the opinion which I had too 

 hastily renounced. In 1852 or 1853, Mr Hugh Miller and Mr 

 Robert Chambers discovered whole acres of blocks embedded 

 in the clay between Leith and Joppa, all striated in one uni- 

 form direction (E.N.E. and W.S.W.), which agrees correctly 

 with the striation of the fixed rocks in the neighbourhood. 



If we infer the ancient existence of glaciers, and the direc- 

 tion in which they moved, from the parallel striae on rocks in 

 situ, we cannot refuse to receive the parallel striation of blocks 

 embedded in a matrix of clay, as evidence of the same import. 

 I have no doubt, then, that when the subsoil of the plain below 

 Corusk is exposed, embedded blocks will be found in it, and 

 striated in the direction of the valley, namely, N.W. by N., 

 and S.E. by S. Upon these, as a floor or bottom, the glacier 

 had moved, and the mounds D, E, F, are remnants of its ter- 

 minal moraines, that is, of the clay, sand, gravel, and blocks, 

 which being borne on its surface, were dropped over its lower 

 end, and perhaps afterwards pushed before it. With regard 

 to the mound C, its smooth sloping sides give it a different 

 character, and render it probable, that it is merely a protube- 

 rant portion of the bottom. That bottom may consist of the 

 old stiff boulder clay ; but judging from what is seen on the 

 banks of the river, it more resembles the upper and looser clay, 

 and it may even be the lower portion of the matter constituting 

 the moraines. The semi-fluid constitution of glaciers, as de- 

 scribed and illustrated by Professor Forbes, leads to the con- 

 clusion, that under certain circumstances, they will travel over 

 such a deposit. For, as the clay and gravel of moraines has 

 more than twice the specific gravity of ice, it is evident that 

 the power of a glacier to drive a large mass of such materials 

 before it, must cease at a certain point, since beyond that point 

 it will be easier for the glacier to dilate itself upward, than to 

 overcome the resistance in front. But as it swells upward, the 



