690 THE ICE AGE IN NORTH AMERICA. 



these events with the changes in the eastern portion of the 

 continent, yet the order of sequence is evident ; and that the 

 greater part, if not all, occurred in the Quaternary, is also evi- 

 dent. . . . 



The history of changes shown in these sections is suffi- 

 ciently obvious. In the time of the old river-system, R was a 

 river-bed, doubtless with a ridge on either side represented by 

 the dotted lines. In this bed accumulated gravel, containing 

 gold. Then came the lava-flow, which of course ran down the 

 valley, displacing the river and covering up the gravels. The 

 displaced rivers now ran on either side of the resistant lava, 

 and cut out new valleys, two thousand feet deep, in the solid 

 slate, leaving the old lava-covered river-beds and their aurifer- 

 ous gravels high up on a ridge. In other cases the convulsion 

 which ejected the lava also changed greatly the general slope 

 of the country, and therefore the direction of the streams. In 

 such cases of course the present river-system cuts across the 

 old river-beds and gravels, and their covering lavas, as shown 

 in Fig. 142. 



The age of the old river-gravels is still doubtful ; that of 

 the newer river-gravels is undoubtedly Champlain or early Ter- 

 race. Below we give a list, taken from Whitney, of the re- 

 mains found in these gravels : 



Newer Placers. — Great mastodon, mammoth, bison, tapir 

 (modern), horse (modern), man's works. 



Deep Placers. — Great mastodon,* mammoth, tapir (mod- 

 ern), rhinoceros (ally), hippopotamus (ally), camel (ally), horse, 

 extinct species. 



It will be seen that the fauna of the deep placers unite Pli- 

 ocene and Quaternary characters. The great mastodon, the 

 mammoth, and the tapir, are distinctively Quaternary, while 

 the others are Pliocene. The plants, according to Lesquereux, 

 are decidedly Pliocene. Therefore Whitney has not only placed 

 the deep placers in the Pliocene, but made them the repre- 

 sentative of the whole Pliocene, and probably Miocene, and 

 the lava-flow as the dividing-line between the Tertiary and the 





* Whitney states that the mastodon is not found here, but it has been 

 since found. 



