PREFACE 



To the memory of Huxley as my chief teacher in comparative anatomy, 

 as well as to that of Balfour, my first teacher in embryology, I have dedicated 

 this work. Huxley set forth the logic of Darwin as applied to palaeontology ; 

 Balfour's genius was beyond imitation, but his pupils may follow the example 

 of his ardent enthusiasm and his genial way of living the life of science. 



Only a few men of the last century had the gift of speaking in clear 

 language both to the learned and unlearned, and the greatest of these was 

 Huxley. To write both for the man of one's own profession and for the 

 layman, to be accurate and abreast of the specialist who knows as much 

 or more of a subject than you do, while intelligible to the non-specialist — 

 there is the difficulty. Many times have I thought to myself in the course 

 of the preparation of these and similar lectures how simple it would be 

 to address either audience separately. Yet I consider it fortunate that both 

 are with us, because I share Huxley's confidence in addressing those who 

 are willing to do a little serious thinking in order to enjoy the vast vistas 

 of interesting truth which come as the reward of effort. I share also his 

 conviction that it is the duty of the man of science to devote a certain part 

 of his time, however absorbed in research he may be, to an honest attempt 

 to scatter scientific truth. Although I may not claim that any parts of this 

 volume are light reading, I have endeavored both to hold the attention of 

 those who are already within the charmed temples of palaeontology and to 

 attract new votaries to its shrines. It should, however, be clearly understood 

 that considerable sections of this work are purely documentary and may 

 be passed over rapidly by the general reader. 



Time and place are the main theme of this work rather than descent, 

 which has been the main theme of all previous general treatises on the 

 Caenozoic mammals ; it is a study of the sources or birthplaces of the several 

 kinds of mammals, of their competitions, migrations, and extinctions, and 

 of the times and places of the occurrence of these great events in the world's 

 history. To set forth this history in all its grandeur, it is interesting to 

 consider the question of past environments, such as the past geography 

 (palaeogeography) of the earth, the changes in climate and in the earth's 

 surface which conditioned the evolution of plant life (palaeobotany) as the 

 primary source of food supply for the mammals. Thus geolog}^, geography, 

 botany, and climate are treated as leading to a clear understanding of each 

 of the successive groups and movements of mammalian life. 



In a way this work marks the completion of a special line of study 



