August 21, 1914] 



SCIENCE 



275 



in the narrow field of tlie British Isles to 

 convince him that there were distinct inter- 

 glacial stages, and, unfortunately, he assumes 

 that the evidence of such interglacial stages 

 is inconclusive in any part of the world. In 

 this and other matters he displays a distinctly 

 sophomoric air. Thus on page 124 he an- 

 nounces : 



" The elaborate systems of the older inter- 

 glacialists may all be set aside as unproved. 

 The class of evidence on which they were 

 founded will not stand critical examination. 

 For instance, the superposition of different 

 sheets of till may at the most mean change in 

 the direction of ice movement. The occur- 

 rence of interbedded gravels may merely mean 

 local oscillations, or may be due to the natural 

 formation of subglacial gravels between the 

 ground moraine and englacial moraine. Fos- 

 siliferous beds between beds of boulder clay, 

 unless they are clearly proved to be still in 

 the position in which they were deposited, may 

 have been caught up from the preglacial floor. 

 The greater weathering of the older drift 

 sheet may have been effected while the newer 

 sheets were being deposited. It will thus be 

 seen that it is a distinctly difficult thing to 

 prove an interglacial period. We must, how- 

 ever, as Mr. Lamplugh has long maintained 

 (Presidential Address to the Geological Sec- 

 tion of the British Association, 1906), get 

 back to solid ground in this miatter before it 

 is possible to make any real advance. There 

 have been altogether too many speculations 

 and too many loose correlations from place to 

 place in dealing with this problem. We are 

 bound to take our stand on the comparatively 

 simple monoglacial hypothesis until we can 

 prove at least one interglacial period. It wiU 

 then be time enough to proceed to consider 

 further possibilities." 



That there are glacialists in the world who 

 have been carefully considering all these 

 matters in a long experience in field studies, 

 and have been properly evaluating the field 

 evidence, seems not to have dawned upon the 

 author of this volume. 



The contrasts in the amount of denudation 

 displayed by the older and newer drifts of the 



British Isles is clearly set forth by the author, 

 but he takes the position that these contrasts 

 can not be used as a time measure because 

 climatic conditions have not been uniform. It 

 is probable, however, that in the British Isles, 

 as in other glaciated districts, a careful study 

 of drainage features would serve to make 

 clear whether a given valley had been formed 

 rapidly by a larger stream than the present 

 drainage line, and especially if it was in use 

 as a line of glacial drainage. The work of 

 streams which headed in the ice sheet may 

 thus be compared with that of contemporary 

 streams which had no contributions from the 

 ice. Comparison may also be made between 

 the work along a given drainage line accom- 

 plished by glacial drainage, and that accom- 

 plished after the ice had ceased to contribute 

 water to it. To set aside as of no value 

 studies of weathering and erosion of drift 

 sheets, as is done in the quotation given below, 

 seems a departure from the spirit of true 

 scientific investigation. The following state- 

 ments appear on pages 75-76: 



" The southern boulder clay plains are ex- 

 tensively dissected by a system of valleys 

 which have for the most part come into exist- 

 ence since the abandonment of the district 

 by the ice. These valleys frequently trench 

 through into the underlying rocks, and the 

 boulder clay thus comes to occupy the inter- 

 stream areas. When, as for example in Not- 

 tinghamshire, the underlying rocks are exceed- 

 ingly soft and denudation has been especially 

 severe, more extensive removal of the surface 

 has resulted in the drift only remaining as a 

 capping to more or less isolated hills. 



" This extensive denudation and maturity 

 of drainage which characterizes the older drift 

 is suggestive of a very considerable lapse of 

 time since its exposure to subaerial erosion. 

 Moreover, the denudation exhibited by the 

 more northerly drift is trivial in comparison. 

 We might draw from this the conclusion that 

 the interval between the laying bare of the 

 older and newer drift was immensely longer 

 than post-glacial time were it not that we have 

 to do with very different climatic conditions 

 in the two periods. There is every reason to 



