Book Notices. 113 



Book Notices. 



The Canadian Ice-Age. By Sir J. William Dawson, 

 C.M.G., F.R.S. (Montreal: Wm. Y. Dawson. JSTew 

 York and London : The Scientific Publishing Com- 

 pany, 1893.) 



It is continually brought to the notice of geologists that the most 

 recent period in the long history of the earth is also that which 

 excites the greatest controversy. We can deal complacently with 

 earth-movements, mountain-thrusts, and submergences of half a 

 continent, so long as the organisms affected by these occurrences 

 are less specialized mammals than ourselves; but we find it hard 

 to believe in great physical or climatic changes within the limits 

 of our own written or unwritten history. Moreover, our knowledge 

 of the post-Pliocene period is burdened with an excess of detail; 

 and broad and sweeping generalizations seem at present out of the 

 question. And, if we go one step further, we may fairly attribute 

 our friendly agreement with regard to the conditions of the older 

 periods to our ignorance rather than to our information. 



Sir William Dawson, in the present work, summarizes several 

 previous papers of his own, just as M. Gaudry's detailed memoirs 

 were summarized for general use in " Les Ancetres de nos Ani- 

 maux." This handy paper-bound volume deals strictly with Can- 

 ada, and is in no way a "Theory of the Earth." It is moderate in 

 tone, and forms a serious plea for a rational treatment of the glacial 

 epoch. Whatever caused the cold conditions in the northern hemi- 

 sphere, or in parts of the northern hemisphere, it is pointed out 

 that the land-ice in Canada radiated from two local centres, and 

 not from the hypothetical ice-cap at the pole. Readers of Nature 

 will remember the evidence brought forward by Dr. G. M. Dawson 

 as to the " Laurentide " centre of glaciation on the east and the 

 " Cordilleran " centre on the west {Nature, vol. xlii., p. 650). The 

 conditions maintained by Sir W. Dawson as most favourable to the 

 development of glaciers are high masses of land in proximity to 

 cold seas ; and, as he properly points out, these conditions still 

 prevail in North America to a greater extent than in North Europe. 

 They prevail, moreover, in Greenland, but not in Grinnell Land, 

 to cite two closely neighbouring areas. 



It will be clear, then, that Sir W. Dawson urges that differential 

 earth-movement was the main factor in the production of Canadian 

 glaciation. The evidence of marine shells in the drift, of the 

 bones of whales, of the character of the deposits themselves, all 

 points to the existence of wide areas of submergence. With regard 



