114 LAKES OF NORTH AMERICA. 



Of the remains of vertebrates, the bones of the mastodon or mammoth, 

 and of the ox, camel, and horse have been found in the sediments of Lake 

 Lahontan, together with a single undetermined fish. The bones of a 

 musk-ox were obtained near Salt Lake City under such conditions that it 

 is believed they were buried in the upper strata of the Bonneville sedi- 

 ments. The basins of contemporaneous lakes in Oregon, have yielded 

 vertebrate fossils more abundantly, but concerning these there are differ- 

 ences of opinion as to their age. It is probable that some of them at least, 

 and perhaps the larger portion, were washed out of older deposits and 

 accumulated in the l)asin where they are now found. 



In the sediments of both Bonneville and Lahontan there are many 

 species of fresh-water shells, but these are usually small individuals, and 

 appear to have lived under uncongenial conditions. 



The remains of animal life do not seem to point to any very definite 

 conclusion. We are led to believe from all of the evidence available, 

 however, that the climate of the lake period was cold and changeable, 

 and consequently uncongenial to either plant or animal life. The inter- 

 lacustral epoch was probably a time of high temperature and aridity. 

 The large animals whose bones have been discovered may have been 

 forced to migrate owing to wide-reaching climatic changes, and were per- 

 haps only temporary visitors to the region where they succumbed to ad- 

 verse conditions. 



The mastodon and mammoth roamed over nearly the whole of North 

 America during Pleistocene times, but have since become extinct. The 

 camel is no longer found on this continent, and the horse was extinct 

 before the coming of the white man. The musk-ox is now found only 

 far to the north. 'The extinction of some of these large animals, and 

 the scattering of others to distant regions, suggests the lapse of a long 

 period of time since they lived together where their remains are now 

 found, and also points to great changes in climatic and other elements of 

 their environment. 



Of the presence of man on the shores of lakes Bonneville and Lahon- 

 ton the records are silent. 



Lakes of the Remote Past. 



The presence of tlie bones of large animals in the sediments of lakes 

 Bonneville and Lahontan naturally leads one to look farther back in 

 the earth's history, to the deposits of other lakes from which a vast 



