PRESIDENT'S ADDRESS. 17 



successive. Here also the lower clay cannot be traced very far inland, 

 eastward or southward; the others have a wider extension, but they 

 reach a greater elevation above sea-level than on the eastern side of 

 England. The sand is inconstant in thickness, being sometimes hardly 

 represented, sometimes as much as 200 feet. The upper clay runs 

 on its more eastern side up to the chalky boulder clay, and extends 

 on the south at least into Worcestershire. On the western side it 

 merges with the upper member of the drifts radiating from the moun- 

 tains of North Wales, which often exhibit a similar tripartite division, 

 while (as we learn from the officers of the Geological Survey) boulder 

 clays and gravelly sands, which it must suffice to mention, extend from 

 the highlands of South Wales for a considerable distance to the south- 

 east and south. Boulder clay has not been recognised in Devon or Corn- 

 wall, though occasional erratics are found which seem to demand some 

 form of ice-transport. A limited deposit, however, of that clay, con- 

 taining boulders now and then over a yard in diameter, occurs near 

 Selsey Bill on the Sussex coast, which most geologists consider to have 

 been formed by floating rather than by land ice. 



Marine shells are not very infrequent in the lower clays of East 

 Anglia and Yorkshire, but are commonly broken. The well-known 

 Bridlington Crag is the most conspicuous instance, ' but this is ex- 

 plained by many geologists as an erratic — a piece of an ancient North 

 Sea bed caught up and transported, like the other molluscs, by an 

 advancing ice-sheet. They also claim a derivative origin for the organic 

 contents of the overlying sands and gravels, but some authorities 

 consider the majority to be contemporaneous. Near the western coast 

 of England, shells in much the same state of preservation as those on 

 the present shore are far from rare in the lower clay, where they are 

 associated with numerous striated stones, often closely resembling those 

 which have travelled beneath a glacier, both from the Lake District 

 and the less distant Trias. Shells are also found in the overlying sands 

 up the valleys of the Dee and Severn, at occasional localities, even as 

 far inland as Bridgnorth, the heights of the deposits varying from 

 about 120 feet to over 500 feet above the sea-level. If we also take 

 account of the upper boulder clay, where it can be distinguished, the 

 list of marine molluscs, ostracods, and foraminifers from these western 

 drifts is a rather long one. 1 



Marine shells, however, on the western side of England, are not 

 restricted to the lowlands. Three instances, all occurring over 

 1,000 feet above sea-level, claim more than a passing mention. At 

 Macclesfield, almost thirty miles in a straight line from the head of the 

 estuary of the Mersey, boulder clays associated with stratified gravels 



1 W. Shone, Qtuxrl. Journ. Geol Sec, xxxiv. (1878), p. 383. 



l'JU. Q 



