SOUTH LANCASHIRE, CHESHIKE, AND THE WELSH BORDER. 387 



with the earlier deposit, except that, so far as can be judged from 

 the very limited sections, the materials of which it is composed 

 seem to have travelled also in a north-easterly direction. The 

 discussion of its origin is therefore beyond the scope of this paper ; 

 but it, may be pointed out that the sequence of deposits presents a 

 general similarity to that found in the east of England. The so- 

 called Upper Boulder-clay, or Chalky Boulder- clay of Norfolk *, for 

 example, with the underlying sands and gravels, is comparable in 

 many ways to the marine drifts of South Lancashire and IS'orth 

 Wales. In particular the signs of disturbance of the pre-existing 

 beds, though not so marked as in the Contorted Drift pf the east, are 

 still a noticeable feature below a Boulder-clay in this district. The 

 Cromer Till also, though consisting, of course, like the rest of the 

 East Anglian drift, of different materials, corresponds in its de- 

 scription to the basement-(day of Xorth Wales. Without entering 

 into the question of contemporaneity in the deposits of the east and 

 north-west of England, it may be remarked that a somewhat 

 similar sequence of events is indicated in the two areas. The 

 Cromer Till is usually regarded as the product of an ice-sheet, the 

 sands and gravels as indicating an intergiacial period of submergence, 

 while the Upper or Chalky Boulder-clay is attributed by various 

 authors to an ice-sheet or coast-ice. 



The importance of the fact that the newer drifts of the north- 

 west are made up of alternations of Boulder-clay and sand and 

 gravel consists in this, that on the ice -sheet theory of the origin of 

 the Boulder-clays, it must be supposed that either the sea-bed was 

 repeatedly invaded by an ice-sheet, or that the land underwent 

 repeated oscillations of level. In either case it would seem as if the 

 beds and the evidence of each change should have been more widely 

 spread. But nothing is more strongly impressed upon us by a careful 

 drift-survey of this district than the impossibility of correlating the 

 details of one section with those of another, unless in the immediate 

 neighbourhood. The constantly varying conditions which seem to 

 have prevailed, and the evidence of different conditions having held 

 in neighbouring localities at the same time, seem to point to the 

 action of floating ice driven by tidal or oceanic currents. During the 

 time of even the greatest submergence Snowdon and the surrounding 

 hills must have stood well above water, and on the south and south- 

 east islands both large and small must have been numerous. By 

 such a group the prevailing currents from the north would be 

 deflected, to the south-west over Anglesey on the one side, and to 

 the south-east over the plains of Cheshire and Shropshire on the 

 other, while within the limits of the group a local circulation might 

 be maintained. 



* For a general account of the Norfolk Drifts, see " The Glacial Drift ol" 

 Norfolk," \)j H. B. Woodward, Proc. Geol. Assoc, vol. ix. no. 3, p. Ill 



(1885). 



