[Footnote 109: The glacial literature of our own island only, is so extensive that the student may well be bewildered when he attempts to grapple with it. He is recommended to read the following general works: J. Geikie, _The Great Ice Age_. 3rd Edition, 1894. H. Carvill Lewis, _The Glacial Geology of Great Britain and Ireland_. 1894. G. F. Wright, _Man and the Glacial Period_, 1892, and _The Ice Age in North America_, 1890. Sir C. Lyell, _Antiquity of Man_. 4th Edition, 1873. For the glacial geology of special regions the following papers may be consulted: _The Lake District and adjoining neighbourhood._ E. H. Tiddeman, "Evidence for the Ice Sheet in North Lancashire &c." _Quart. Journ. Geol. Soc._, vol. XXVIII. p. 471. J. G. Goodchild, "Glacial Phenomena of the Eden Valley &c." _Quart. Journ. Geol. Soc._, vol. XXXI. p. 55, and J. C. Ward, _Mem. Geol. Survey_, "The Geology of the Northern half of the Lake District." _Yorkshire._ G. W. Lamplugh, "Drift of Flamborough Head," _Quart. Journ. Geol. Soc._, vol. XLVII. p. 384. _Lincolnshire._ A. J. Jukes-Browne, _Quart. Journ. Geol. Soc._, vol. XXXV. p. 397 and XLI. p. 114. _East Anglia._ Clement Reid, _Mem. Geol. Survey_, "The Geology of the district around Cromer." _North Wales._ T. McK. Hughes, "Drifts of the Yale of Clwyd" &c. _Quart. Journ. Geol. Soc._, vol. XLIII. p. 73, and A. Strahan, "Glaciation of South Lancashire, Cheshire, and the Welsh Border," _ibid._, vol. XLII. p. 486. _Switzerland._ C. S. du Riche Preller, "On Fluvio-glacial and Interglacial Deposits in Switzerland," _Quart. Journ. Geol. Soc._, vol. LI. p. 369 and "On Glacial Deposits, Preglacial Valleys and Interglacial Lake formations in Sub-Alpine Switzerland," _ibid._, vol. LII. p. 556. The reader will find references to other works on the Glacial Geology of other districts by consulting the general works referred to on the preceding page.] The foregoing remarks will convince the student that any attempt to show the distribution of land and sea during any part of the glacial period is not likely to meet with general acceptance, as so much depends upon the terrestrial or marine origin of the deposits of the lowlands, and the mode of formation of the shell-bearing drifts of high levels. The occurrence of elevation to a greater height than that which our country at present possesses during portions at any rate of the glacial period has been inferred on general grounds, but direct evidence in favour of it is furnished by the existence of a number of ancient valleys on the land around our coasts, whose floors are often considerably below sea-level, while the valleys are now completely filled up with glacial accumulations, except where they have been partially re-excavated by streams which for some distance run above the courses of the ancient streams.