VuousT 31, ISSiJ.i 



SCIENCE. 



•275 



There are, no doubt, characters by which such and 

 such shoes could be distinguished from other slioes, 

 tliese bullies from other bottles; but it is aNo triu-, 

 that we have, in recent forms of life in zoology and 

 Ixilany, irrefragable proofs of the melamuriihoses, 

 and transformations, and cliauges of the species, in 

 accordance with the doctrine with which we com- 

 menced. 



We now come to the second chapter of our subject. 

 With the assumption, as I take it already satisfac- 

 torily proven, of species having changed over into 

 others, in considering this matter of geological suc- 

 cession 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. 



1 have on the board a sketch or table which repre- 

 sents the changes which took place in certain of the 

 mammalia. I give you a summary of the kind of 

 tiling which we find in one of the branches of pale- 

 ontology. I have hi-re two figures, one represent- 

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

 two extinct species lliat belong to the early eocene 

 periods. One represents the ancestor of the horse 

 line, Ilyracotherium, which has four toes on his an- 

 terior feet, and three behind; and the other, a type 

 of animal, Phenacodus, which antedated all the 



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 inlerniediate forms will be found. 

 1 have frequently hail the ple.isure of realizing anti- 

 cipations of Ihis kind. I have asserted that certain 

 types would be found, and they have been found. 

 Vou will see that I attend to the matter of time 

 closely, because there have been a great many things 

 discovered in the last ten or fifteen years in this de- 

 partment. In these forms I give the date of the dis- 

 covery of the fauna in which they are embraced. 



Here we have the While-Klver fauna discovered In 

 1S.5U; then we skip a considerable period of time, and 

 the next one was in 1869, when the cretaceous scries 

 was found. Si.x or seven cretaceous faunae have 

 been found. Then we have the Hridger fauna in 

 ISTOj tlie Wasalch fauna in 1874. Next we have, in 

 1S77, the Eqiius beds, and the fauna which they em- 

 brace, which also was found in 1S78. The Permian 

 fauna, which is one of the last, is 1879: and the last, 

 the Puerco, which gives the oldest and ancestral 

 types of the modern forms of mammalia, was oidy 

 found In 1881. When I first commenced the study of 

 this subject, about lytiO, there were jwrhaps 'S>0 spe- 

 cies known. There are now something near 2.()tK), 

 and we are auguienting them all the time. I have 



horse series, the elephant series, the hog, the rhi- 

 noceros, and all of the other series of hoofed ani- 

 mals. Eiich presents us with the primitive position 

 in which they 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 priiicip.al epochs of the mesozolc 

 times, and six of the leading ones of the tertiary lime. 

 I have a<lded some da" > to show you the time when 

 the faunae which are entombed in those beds wi-re 

 discovered, in the course of our studies; and yon will 

 easily see how unsafe it is to say that any given ty|>e 

 of life has never existed, and assert that such and 

 such a form is unknown; and It Is still more unsafe, 

 - think, to assert that any given form of life properly 



found many myself: If they were distributed through 

 the days of the year, I think in some years I should 

 have had several every day. But the .iceesslons to 

 knowledge which are constantly being made make it 

 unsafe to Indulge In any prophecies, that, because such 

 and such things have not been fouiul, therefore such 

 and such things cannot be ; for we find such and 

 siu'h things really have been and really are discov- 

 ered. 



The successive changes tliat we have In the mam- 

 malia have taken pl.ace in the feet, teeth, and brain, 

 and the vertebral eolunui. The )>arls which present 

 us the greatest numbers of variations are tho.se In 

 which many parts are concerned, as in the limbs and 

 feet. In liie lower eocene (Puerco), the toes were 



