IV PREFACE TO THE THIRD EDITION. 



evolution is kept more prominently in view. The subjects of Devonian 

 fishes and of Carboniferous Conifers are rewritten, and the origin of 

 birds and mammals more fully discussed. In the Cretaceous, the Co- 

 manche series of Hill and the Potomac series of McGee are discussed, 

 and figures of characteristic forms given. The Laramie, on account of 

 its peculiar interest as a transitional period, is treated separately, and 

 figures of characteristic forms are given. In the Tertiary the subject 

 of the mammalian fauna of America is mostly rewritten, and the genesis 

 of existing orders, families, genera, etc., more fully discussed. In the 

 Quaternary the evidences of continental elevation, the existence of an 

 ice-sheet, with its terminal moraine, and the Great Lakes formed during 

 its retreat, are more fully given. The Quaternary, on the west side of 

 the continent, is rewritten, the order of presentation changed, and new 

 matter introduced, especially the evidences of continental elevation 

 and of rejuvenescence of the rivers by Sierra elevation. Lender causes 

 of glacial climate, I give greater prominence than before to geographi- 

 cal changes. Changes of climate and of Physical Geography, as the 

 cause of the present distribution of organisms, are somewhat fully dis- 

 cussed, and several examples given and explained. In the chapter on 

 the Psychozoic era the most recent discoveries of human remains and 

 implements, both in Europe and America, are given, and their signifi- 

 cance discussed. 



To the geologists of America, who have freely helped and encour- 

 aged me, and especially to gentlemen connected with the L^nited States 

 Geological Survey, I take this opportunity of acknowledging my deep 

 indebtedness. 



Berkeley, Cal., January, 1891. 



