79 o THE POPULAR SCIENCE MONTHLY. 



shells in tolerable abundance, the most celebrated being at Moel 

 Tryfaen, on the west side of Snowdon, at a height of more than 

 thirteen hundred feet. Shell-bearing drifts have also been found 

 near Macclesfield at a height of over eleven hundred feet, and to 

 the east of Manchester at between five and six hundred feet eleva- 

 tion. Others have since been found on Gloppa, a hill near Os- 

 westry. The fact that the shell-bearing gravels of Moel Tryfaen 

 are nearly forty feet thick shows that, if they are due to sub- 

 mergence, the land must have remained stationary at that level 

 for a considerable period of time, and there would probably be other 

 stationary periods at lower levels. Yet nowhere in the valleys or 

 on the hill slopes of Wales, or the Lake District, or in the English 

 lowlands are there any of the old beaches or sea cliffs, ormarine de- 

 posits of any kind, that must have been formed during such a sub- 

 sidence and which can hardly have been everywhere cleared away 

 by subsequent glaciation. Another difficulty is that the shells of 

 these drifts are such as could not have lived together on one spot, 

 some being northern species, others southern, some frequenting 

 sandy others muddy bottoms, some which live only below tidal 

 water while others are shore species. And, lastly, they are very 

 fragmentary, only a small percentage of entire shells being found. 

 In consequence of these various difficulties it was suggested by 

 the late Mr. Belt that the great Irish Sea ice-sheet had carried up 

 a portion of the sea-bottom imbedded in its substance, perhaps 

 containing deposits of shells of various periods and thus explain- 

 ing the intermixture of species as well as their fragmentary con- 

 dition. The fact that bowlders and pebbles from Scotland, Ailsa 

 Craig, and Cumberland have been found in the Moel Tryfaen beds 

 almost amounts to a proof that they were so uplifted ; and a recent 

 search has shown that in the other localities where marine shells 

 have been found in drift at great elevations similar foreign rocks 

 occur, rendering it almost certain that the same ice-sheets which 

 have distributed foreign erratics so widely over our country, and 

 which in doing so must have passed over the sea-bottom, have in 

 a few cases carried with them a portion of that sea-bottom, and 

 deposited it with the erratics in the places where both are now 

 found. A full discussion of this point, with replies to various ob- 

 jections, by Mr. P. F. Kendal, will be found in the volume already 

 quoted ; and he has recently adduced a fresh argument against 

 " the great submergence " in the fact that, if it ever occurred, our 

 lowlands must for a long time have formed the bottom of a sea 

 two hundred fathoms deep, yet not a single shell characteristic of 

 that depth has yet been discovered in the drift.* The cumulative 



* Wright's Man and the Glacial Period, pp. 167-175. Also Geological Magazine, No- 

 vember, 1892, pp. 491-500. 



