158 W. Upham—Work of Prof. H. C. Lewis. 
perfectly with the explanation given by Lewis, which indeed had 
been before suggested, so long ago as in 1874, by Belt and Good- 
child! This removes one of the most perplexing questions which 
glacialists have encountered, for nowhere else in the British Isles is 
there proof of any such submergence during or since the Glacial 
period, the maximum known being 510 feet near Airdrie in Lanark- 
shire, Scotland.? At the same time the submergence on the southern 
coast of England was only from 10 to 60 feet,? while no traces of 
raised beaches or of Pleistocene marine formations above the present 
sea-level are found in the Shetland and Orkney Islands.* The work 
and writings of Professor Lewis emphasize the principle that 
glacially transported marine shells and fragments of shells, which 
occur in both the till and Boulder-clay and the modified drift in 
various parts of Great Britain, are not to be confounded with shells 
imbedded where they were living or in raised beaches, for only these 
prove the former presence of the sea. 
The drift deposits of England south of the terminal moraines 
traced by Lewis were regarded by him as due to floating ice upon 
a great freshwater lake held on the north by the barrier of the ice- 
sheet which covered Scotland, Northern England and the area of 
the North Sea, and on the south-east by a land barrier where the 
Strait of Dover has been since eroded. Under this view he attri- 
buted the formation of the Chalky boulder-clay in Hast Anglia, and 
of the Purple and Hessle boulder-clays in Lincolnshire and much of 
Yorkshire, to lacustrine deposition. But shortly after the British 
Association meeting in 1887 his observations on Frankley Hill in 
Worcestershire and thence westward°® led him to accept the con- 
clusion, so thoroughly worked out by other glacialists both in 
America and Great Britain, that there were two principal epochs of 
glaciation, divided by an interglacial epoch when the ice-sheets 
were mostly melted away. There can be little doubt that the con- 
tinuation of Lewis’s study of the drift in England, if he had lived, 
would have soon convinced him of the correctness of the opinions 
of Searles V. Wood, jun., Mr. Skertchly, and James Geikie,® that 
land-ice during the earlier glacial epoch overspread all the area of 
the Chalky boulder-clay, extending south to the Thames. Small 
portions of Northern England, however, escaped glaciation both 
then and during the later cold epoch, when the terminal moraines 
mapped by Lewis were accumulated; and these tracts of the high 
moorlands in Hastern Yorkshire and of the eastern flank of the 
1 Nature, vol. x. pp. 25, 26, May 14, 1874; Guon. Mace. Dec. II. Vol. I. pp. 
496-510, Nov. 1874. <A similar opinion was held fifty years ago by Mr. James Smith 
(Researches in Newer Pliocene and Post-Tertiary Geology, pp. 11, 16), though he 
attributed the drift to debacles instead of glaciation. 
2 Quart. Journ. Geol. Soc. vol. vi. 1850, pp. 386-8; xxi. 1865, pp. 219-21. 
3 Quart. Journ. Geol. Soc. vol. xxxiv. 1878, pp. 454-7; xxxix. 1883, p. 54. 
Grou. Mac. Dec. IL. Vol. II. 1875, p. 229; Dee. II. Vol. vi. 1879, pp. 166-72. 
* Quart. Journ. Geol. Soc. vol. xxxv. 1879, p. 810; xxxvi. 1880, p. 663. 
5 Grout. Mae. Dec. ILI. Vol. LV. pp. 515-17, Nov. 1887; Vol. V. p. 480, 
Sept. 1888. 
6 Quart. Journ. Geol. Soc. vol. xxxvi. 1880, pp. 468-500; Great Ice Age, 
second ed. pp. 360-860. 
