54 MR SMITH ON THE CHANGES 



in it, much broken, and deprived of their colour. Mr 

 Trimmer, in describing the diluvial deposits in Caernar- 

 vonshire, in the proceedings of the Geological Society,* 

 states that he found broken shells in the diluvium of the 

 low cliff near Beaumaris. He also found broken shells in 

 a bed of sand, on the summit of Moel Try fane, 1400 feet 

 above the level of the sea. The expression seems to imply 

 alluvial rather than diluvial agency. Mr Trimmer, how- 

 ever, informs me that he ascribes their presence at so high 

 an elevation to the latter cause, the beds having all the 

 appearance of violent action, and the subjacent rocks worn 

 and scratched by friction of transported pebbles. Mr 

 Phillips also is inclined to think that in Holderness the ir- 

 regularity of deposition of the shelly gravel seems to point 

 to diluvial currents rather than to change of level, t 



It is not, therefore, a necessary inference that the mere 

 discovery of sea-shells at high levels is a proof of permanent 

 submergence. Their fragments, like those of coal, sand- 

 stone, and shale, mark that the distance from which they 

 have been transported is a short one. It is only when found 

 in situ in regularly stratified beds that we are entitled to 

 draw such conclusions; but their presence in diluvial beds 

 must be held as an exception to the general rule. 



Although this is not the place to offer any speculation 

 respecting the origin of the till, I think it evident that it 

 must have arisen from causes altogether different from those 

 which have produced the marine alluvia. Whatever they 

 were, they must have been violent and transitory. Of their 

 violence we have ample proof in the size of the fragments 

 they have transported, as well as the erosion of the rocks 

 over which they have passed, but that they suddenly ceased 



* Vol. i. p. 332. t Treatise on Geology, p. 198. 



