376 O. C. Marsh— Vertebrate Life in America. . 
assurance of a friend who had os Pearse them in New 
Mexico, to convince me that they were not from the mounds. 
A third fact, -~ I leave Man to the dy Se nat Vea on whose 
province I am even now trenching. In a large collection of 
waterjars from Peru, th at no one could fainty d douks that some 
intercourse had taken place between the widely separated peo- 
ple that made them 
The oldest known remains of Man on this continent differ 
in no important characters from the bones of the typical 
Indian, although in some minor details they indicate a muc 
more primitive race. ‘These early remains, some of which are 
true fossils, resemble much more closely the corresponding 
parts of the highest Old World Apes, has do the latter our 
Tertiary Primates, or even the recent American Monkeys. 
a living and fossil forms of old world Primates fill up 
so etek long survive. Texts the intermediate forms of 
the past, if any there opal become of still —. gc 8 
For such missing links, must look to the caves and later 
b] 
left their remains somewhere on this continent. In these two 
directions, as I believe, lie the most important future discov- 
eries in Paleeontology. 
As a cause for many changes of structure in mammals 
during the Tertiary and Post-Tertiary, I regard, as the most 
. potent, Natural Selection, in the broad sense in which that term 
1s now used by American evolution ists. Under this head, I 
include not merely a Malthusian struggle for life among the 
animals themselves, but the equally important contest with the 
elements, and all surrounding nature. By changes in the envi- 
ronment, migrations are enforced, slowly in some cases, rapidly 
in others, and with change of locality must come adaptation to 
new conditi tions, or extinction. The life-history of Tertiary 
mammals illustrates this nar at every stage, and no other 
explanation meets the fac 
