34 R. M. Deeley—The Glacial Succession. 
absence of great glaciers in the British Isles, and the Scandinavian 
glacier passed unchecked up the easterly valleys of England towards 
the central watershed ; for the Chalky Boulder-clay becomes a mere 
silt with an occasional flint in such sheltered places as Market Bos- 
worth and Abbots Bromley. It must also be remembered that when 
the mountains of the British Islands were well out of the water and 
nourished great glaciers, the moisture-laden south-westerly winds 
would be precipitated in some measure before they reached the 
Scandinavian peninsula, whereas when these islands were partly 
submerged the precipitation would be on the continental uplands, 
and the Scandinavian glaciers would reach their greatest develop- 
ment. The chalky gravel which rests upon the chalky clay and 
encumbers all, or almost all, the southerly and westerly watershed 
of the Trent does not contain molluscan remains, although the ice- 
sheet of that date presumably passed over the floor of the German 
Ocean, yet to the west of the watershed, and in such straits as those 
of Silverdale and Biddulph, shell fragments are very numerous. 
Why, if the Scotch, Irish, and Cumbrian ice-sheet was able to form 
shell gravels at a height of 1360 feet in Wales, 1200 feet in Wick- 
low, and 1150 feet at Macclesfield, was it unable to form them in 
the central, south-eastern, and northern portions of the Trent Basin ? 
And why was the Scandinavian glacier unable to form shell gravels 
in Kast Leicestershire? The gravels and sands are there in force, 
but not the shells. Rather the high level gravels of Wales are truly 
marine deposits, and the flints they contain were carried from the 
east by bergs carved from the Great Scandinavian Glacier which 
occupied the easterly valleys of Eugland and not from Antrim. 
According to this view the gravels were formed partly during mild 
and partly during cold conditions of climate. One explanation of 
the absence of molluscan remains in the gravels to the east of the 
central watershed is that the Straits of Dover were not very wide, 
and that the northern part of the German Ocean was blocked by ice, 
leaving the enclosed area too brackish for mollusca to flourish in, 
and also that in interglacial times the German Ocean was dry land. 
Professor Geikie’s third epoch, a glacial one, would therefore seem 
to require further subdivision into five distinct epochs marked by a 
possibly continuous but varying depth of submergence. There is 
no proof, other than that furnished by the widespread nature of 
both the sands and Boulder-clays, and their marked lithological 
peculiarities, that these epochs indicate great climatic changes, but 
the evidence is distinctly in favour of such a supposition. From 
the table showing “The Glacial Succession” it will be seen that 
this means seven distinct cold epochs. 
On the advent of warmer conditions, at the close of Middle 
Pleistocene times, Britain was again elevated, and the Trent began 
to deposit its high-level gravels, and clear ont the Boulder-clays 
from its valley. Some of these gravels are between 70 and 80 feet 
above the alluvial plains of the present valley, and all terraces 
above about 30 feet show signs of great surface disturbance. From 
the trend of the ridges and furrows of these surface deposits 
