•290 
LAMPLUGH : GLACIAL SECTIONS NEAR BRIDLINGTON. 
It is well known how keen has been the discussion as to the 
origin of the high-level shelly drifts of ^loel Tryfaen, Macclesfield, 
and other places, and if it can be shown that the ice which reached 
these places was charged, as that of East Yorkshire seems almost 
certainly to have been, with the spoils of a sea bottom, the explana- 
tion of the shelly drift will be simple enough. 
Another feature which may be explained by the formation of the s 
Boulder-clay from the bed of an Arctic sea is the above-mentioned 
extraordinary diversity of the boulders. As Keid has pointed out," 
the gathering in of these boulders has evidently been a complex 
process. The presence in the Boulder-clay of well-rounded beach- 
pebbles, and of Pholas — and Saxicava — bored limestones proves that 
many of the erratics must have lain for some time on a sea-bottom, 
whither no doubt they were dropped in the first place by floating ice, 
for the fauna of the sli ell-beds, the character of their pebbles, and 
other signs are convincing evidence for the rigorous climate which 
prevailed during their formation. And before the land ice reached 
any given area of this sea-bottom, we may be sure it had been crossed 
and re-crossed by the floating ice with which the enclosed North Sea 
must have been cumbered. This floating ice, carried hither and 
thither by wind and tide, would scatter its burden at random, and 
cause a very miscellaneous accumulation even before the passage of 
the land-ice ; which, in turn, would intensify the diversity partly by 
the addition of new material, and partly by still further mingling the 
old. Wherefrom it follows that we must not place much confidence 
in the evidence gleaned from the erratics as to the actual direction 
and distance which the ice-sheet has traversed. 
It has been for many years a favourite opinion of glacialists that 
our Yorkshire Drifts are, as a whole, newer than those of Norfolk and 
the Eastern Counties, the supposition being that the more southerly 
region, being nearer the periphery of the ice, preserves beds of older 
date than the area further north, wherein prolonged glaciation is 
supposed to have destroyed all the relics of the earlier stages. 
But I think there are no grounds for this assumption ; and although 
the later Tertiaries are wanting in Yorkshire the reason is that this 
♦ Survey Memoirs, " Cromer," p. 90, " HoldernesB, " p. 43. 
