part 1] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxvii 



over 5000 square miles of land in England and Wales would vanish 

 if the Pleistocene deposits were removed, which represents ahout 

 one-eleventh of the whole country. 1 



There is definite evidence that most of this area was covered 

 temporarily hy the sea shortly before the onset of the glaciation. 

 Some part of it, however, may at that time have been above 

 sea-level, since in certain spots the lowering of the rock-surface to 

 its present level appears to have been effected by glacial erosion — 

 a point to which I shall revert. It is, of course, obvious that the 

 shape of the surface in this portion of our country is dependent 

 entirely upon the Glacial and post-Glacial deposits. 



We have next to consider the tracts, even more extensive than 

 the last, in which the solid rocks, although above sea-level, are so 

 deeply buried under drift that they have practically no effect upon 

 the features, except in providing the concealed foundation. Ground 

 of this kind fringes, more or less broadly, most of the depressions 

 just described ; and expands over wide areas in the Eastern and 

 Midland counties, as well as in Cheshire, Lancashire, and Cumber- 

 land; prevailing chiefly, but not entirely, on the softer clayey 

 formations which are least assertive in themselves as feature- 

 builders. These tracts have usually rather ragged and indefinite 

 limits where they encroach upon the strong feature-building for- 

 mations ; but their broad outlines are readily traceable, and are 

 shown approximately on the map facing p. lxxxii. It will be 

 observed that these blanketing drifts fall distinctly into two 

 groups — an eastern and a Avestern ; and are most continuous where 

 the seaward slopes are gradual. They mark respectively the effect 

 of the ' East British ' ice-sheet, pressing in obliquely from the 

 North-Sea basin, and of the ' West British ' ice-sheet, pressing 

 similarly inward from the Irish-Sea basin. 3 



Ground of this description covers in the aggregate nearly 10,000 

 square miles in England and Wales, which is about a sixth of 



1 These estimates of area have been obtained by measuring- the tracts 

 approximately in each separate sheet of the Geological Survey 1-inch map, 

 and summing the figures. The results are given in round numbers, so as to 

 avoid a fallacious appearance of accuracy ; the figures actually obtained were 

 5350 square miles in this case, and 9930 square miles in that which follows 

 next. 



- See ' Names for British Ice-Sheets of the Glacial Period ' (letter), Geol. 

 Mag. 1901, p. 142. 



e2 



