THE EXTINCT MAMMALIA. 301 



botany, irrefragable proofs of the metamorphoses, and transfor- 

 mations, and changes of the species, in accordance with the doc- 

 trine with which we commenced. 



We now come to the second chapter of our subject. With the 

 assumption, as I take it ah-eady satisfactorily proved, of species 

 having changed into others, in considering this matter of geo- 

 logical succession or biological succession, I bring you face to face 

 with the nature and mode of the change ; and hence we may get 

 a glance perhaps at its laws. 



I have on the board a sketch or table which represents the 

 changes which took place in certain of the Mammalia. I give you 

 a summary of the kind of thing which we find in one of the 

 branches of paleontology. I have here two figures, one represent- 

 ing a restoration, and the other an actual picture, of two extinct 

 species that belong to the early Eocene periods. One represents 

 the ancestor of the horse line, Hyracotherium, which has four toes 

 on his anterior feet, and three behind ; and the other (Plate XIII) 

 a type of animal, Phenacodus, which is antecedent to all the horse 

 series, the elephant series, the hog, the rhinoceros, and all the other 

 series of hoofed animals. It has five toes on all the feet. Each 

 presents us with the primitive position in which their series first 

 come to our knowledge in the history of geological time. 



I have also arranged here a series of some leading forms of the 

 three principal epochs of the Mesozoic times, and six of the lead- 

 ing ones of the Tertiary time. I have added some dates to show 

 you the time when the faunae which are entombed in those beds 

 were discovered, in the course of our studies ; and you will easily 

 see how unsafe it is to say that any given type of life has never ex- 

 isted, or even to assert that such and such a form is unknown ; 

 and it is still more unsafe, I think, to assert that any given form 

 of life properly defined, or that a specific intermediate form of life, 

 will not be found. I think it is much safer to assert that such and 

 such intermediate forms will be found. I have frequently had the 

 pleasure of realizing anticipations of this kind. I have asserted 

 that certain types would be found, and they have been found. 

 You will see that I attend to the matter of time because there have 

 been a great many things discovered in the last ten or fifteen years 

 in this department. Witli these forms I give the date of the dis- 

 covery of the fauna in which they are embraced. 



Here we have the White River fauna discovered in 1850 ; then 

 we skip a considerable period of time, and the next one was in 18G9, 



