542 S. V. Wood,jun. — American and British Surface-Geology. 
between 1100 and 1200 feet, 1 it is clear that either at this time 
or subsequently the submergence must have mucb increased nortb- 
wards and westwards. As, however, tbe mollusca of the Middle 
Glacial sands presents so decidedly an older and more Crag-like 
facies, and even tbe Upper Glacial at Dimlington and Bridlington 
contains tbe Crag forms Nucula Cobboldice and Tellina obliqua, 
wbile tbe Moel Tryfaen and Lancasbire beds contain none but forms 
still liviug in Britisb seas, and one or two more tbat live in tbe 
Arctic Sea immediately nortb of tbe Shetlands, we can bardly 
escape tbe inference that eitber a submergence of tbe Pennine 
region and Nortb Wales took place after the accumulation of the 
earliest portion of tbe Upper Glacial (tbe chalky clay), or eise tbat 
during tbis accumulation those mountain regions were enveloped in 
ice wbicb, until tbe gradual passing away of tbe glacial conditions 
removed it (and tberefore after the chalky and purple clays had 
accumulated), prevented the access of tbe sea and tbe fonnation of 
marine beds. 
Tbe chalky Upper Glacial reaches in Lincolnsbire (Ponton) to 
elevations somewhat exceeding 400 feet, and in Herts of 550 feet, 
and tbe glacier to which it was due, and wbose submarine recession 
most of its accumulation in my view accompanied, descended over 
Lincolnsbire, but could bardly bave extended rauch to the westof the 
meridian which touches the westernmost boundary of tbat countv ; 
because nearly all tbe material which makes up tbis clay is derived 
from the beds of tbat county, from tbe Trias to the Chalk inclusive. 2 
At its greatest extension it existed in tbe form of inland-ice partly 
below the sea-level, just as now occurs in the case of some of the 
inland-ice of Greenland and of parts of Spitzbergen, its eastern edge 
resting upon tbe high ground forming the westernmost parts of 
Norfolk, Suffolk, and Essex, its Southern on tbe nortb border of 
Herts, and its westem, as already defined. Witbin these limits, 
although bere and tbere a few sporadic occurrences of gravel under 
the chalky clay may be detected, and which I refer to some very 
localized current action issuing from tbe ice in its retreat, the 
chalky clay rests directly on tbe older rocks ; wbile on every side of it, 
except tbe north, wbere tbe glacier connected witb tbe place of its 
genesis, tbe sands and gravel s which I term Middle Glacial occur 
extensively, tbougb not uniformly. On its west side tbis glacier 
1 Darbyshire, Geol. Mag. 1865, Yol. II. p. 293. 
2 The Üpper Glacial ot Middlesex and Essex contains little other chalk than the 
hard form of that material characteristic of Yorkshire and Lincolnshire ; but in 
Norfolk a good deal of soft chalk is intermingled, and in the case of the raorainic 
clay in the valleys of that county produced, as mentioned further on, by glaciers pro- 
truding tongue-like from the great mass of inland-ice, the chalk debris seems mostly 
of the soft character of the valley floor on rvhich it rests. The fact that the chalk 
so abundant in the Glacial clay of Middlesex and Essex is all of the hard kind (at 
least if any of the soft is present it is so occasional that it has escaped my notice), 
seems to me to go a long way in proof of this clay not being what Mr. Geikie makes 
it out to be, — the submoraine in situ of a glacier which reached to the Thames 
Valley; for if so the chalk debris would be that derived from the counties of Essex, 
Middlesex, Herts, Cambridge, Sulfolk, and Norfolk exciusively, instead of, as it 
appears to be, chalk derived in chief part, if not exciusively, from Lincolnshire. 
