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as this is by proofs of deep scoring and grooving, which also must 

 have required a vast interval of time for their formation, the period 

 of earlier glaciation must have been one of vast duration. If we 

 accept Mr. Croll's date for the commencement of the Glacial 

 Period, viz., 250,000 years ago, and agree with him that it lasted 

 some 170,000 years, there is no difficulty in accounting for the 

 vast quantity of rock removed from its parent source by glacial 

 action. Whether the earlier part of this period was or was not 

 broken up by interglacial periods of comparative warmth, or whether 

 the succession of events included many oscillations of level of the 

 land there does not seem, in the districts herein specially treated 

 of, any evidence whatever. To find such evidence we have to 

 turn to such districts as East Anglia and the Yorkshire coast, 

 where the later glaciation left many of the deposits of older date 

 undestroyed. What I have contended is that the date when the 

 present distribution of the boulders took place was that period of 

 highest glaciation when the icy flood reached its maximum, and 

 when, debarred an exit by way of the Solway, the ice of Edenside 

 overflowed for some time across the Bewcastle Fells into the Tyne 

 Valley ; across the higher parts of Stainmoor into the Valley of the 

 Tees ; and across the Shap Fells into the basin of the Lune. The 

 relative date of this period can be made out easily enough, and it 

 can be shewn to be contemporaneous with the period when the 

 south-westerly advance of the Scandinavian ice drove the land ice 

 currents in the Midlands south-westward into the basin of the 

 Trent, and reinforced the local sheets of ice, so that they extended 

 as far southward as the Thames Valley before the zone was reached 

 where the rate of melting balanced the supply. In a paper pub- 

 lished in the Proc. Geologists' Assoc, IX., No. 3, in dealing with the 

 question of the age of the Thames Valley Brickearths I have 

 pointed out that their origin, and that of other similar deposits, 

 admits of a simple and ready explanation if we assume that they 

 are due to the ponding back of the waters of the rivers by ice 

 extending southward from Scandinavia. And it is to this period 

 of the invasion of Britain by ice of extraneous origin, coming 

 south-westward by way of Scandinavia on the one side, and south- 



