CHAP. XIT. PROOFS OP SUBMERGENCE. 267 



mountains beneath the waters of the sea is not deficient, as 

 in Scotland, in that complete demonstration which the 

 presence of marine shells affords. The late Mr. Trimmer 

 discovered such shells on Moel Tryfane, in North Wales, in 

 drift elevated 1,392 feet above the level of the sea. It 

 appears from his observations, and those of the late Edward 

 Forbes, corroborated by others of Professor Eamsay and 

 Mr. Prestwich, that about twelve species of shells, including 

 Fusus bamfius, F. antiquus, Venus striatula (Forbes and 

 Hanley), have been met with at heights of between 1,000 and 

 1,400 feet, in drift, reposing on a surface of rock which 

 had been previously exposed to glacial friction 'and striation. 

 The shells, as a whole, are those of the glacial period, 

 and not of the Norwich Crag. Two localities of these shells 

 in Wales, in addition to that first pointed out by Mr. Trimmer, 

 have since been observed by Professor Eamsay, who, however, 

 is of opinion that the amount of submergence can by no 

 means be limited to the extreme height to which the shells 

 happen to have been traced ; for drift of the same character 

 as that of Moel Tryfane extends continuously to the height 

 of 2,300 feet,* 



Rarity of Organic Remains in Glacial Formations. 



The general dearth of shells in such formations, below as 

 well as above the level at which Mr. Trimmer first found 

 them, deserves notice. Whether we can explain it or not, it 

 is a negative character which seems to belong very generally 

 to deposits formed in glacial seas. The porous nature of the 

 strata, and the length of time during which they have been 

 permeated by rain-water, may partly account, as we hinted in 

 a former chapter, for the destruction of organic remains. 



* Eamsay, Quarterly Geological Journal, vol. viii. p. 372, 1852 



