50 LECTURES 



camels in the same manner; and it is a most extraordi- 

 nary picture when we come to study the clearness with 

 which this fossil material will permit us to trace the 

 branching stocks of oxen, deer, antelopes, hogs, and their 

 allies, or the ungulates as they are known, from the gen- 

 eralized common root-stock, the amblypoda, to their 

 modern forms. Other mammalian groups have been 

 worked out in the same way, as far as our discoveries 

 will admit, and doubtless in the future many of the gaps 

 will be filled in, and that is one of the most remarkable 

 chapters in the study of such remains, for the kinships of 

 each new species as it comes to light can be either very 

 closely guessed at, or its affinities are so strikingly 

 apparent, at first glance, as to admit of no manner of 

 doubt in the minds of all biologists. 



It is important to remember, in connection with this, 

 that America, as was the case in other parts of the world, 

 passed through many remarkable physical revolutions 

 during the Tertiary age. In Cretaceous time, or just 

 before the Tertiary, it is known that this country was 

 divided into two great continents separated by a vast and 

 shallow sea covering all that area now familiar 

 to us as the Western Plains and Plateau region. 

 Subsequently mid-continental upheaval took place 

 and this cretaceous sea became slowly obliterated, and 

 the two aforesaid continents joined each other. The 

 tertiary period is now inaugurated by the Eocene epoch, 

 (and the shading of the one into the other, that is, the 

 Mesozoic and Cenozoic was most gradual), during which 

 time great freshwater lakes existed in certain parts of 

 the West, which during the Eocene were drained by 

 continental upheaval. Later Miocene lakes were formed 

 by a corresponding depression over the region of the 

 plains, and still later, toward the close of the same 

 period, the entire coast chain of mountains of the Pacific 

 Coast were formed by an uprising and folding of the sea 

 bottom. Other enormous changes took place, and an 

 authority at my hand states: "That from the end of 

 the Cretaceous to the end of the Tertiary there was a 

 gradual upheaval of the whole western half of the con- 

 tinent, by which the axis, or lowest line, of the great 

 interior continental basin was transferred more and more 

 eastward to its present position, the Mississippi River. 

 Probably, correlative with this upheaval of the western 

 half of the continent was the down sinking of the Mid- 

 Pacific bottom, indicated by coral reefs. Also as a con- 

 sequence of the same upheaval the erosive power of the 



