PSYCHOZOIC ERA— AGE OF MAX— RECENT EPOCH. 603 



tapir, and mylodon, are distinctively Quaternary, while the others are 

 Pliocene. The plants, according to Lesquereux, are decidedly Pliocene. 

 Therefore Whitney has not only put the deep placers in the Pliocene, 

 but made them, the representative of the whole Pliocene, and probably 

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

 and Quaternary. But, all the facts considered, it seems most probable 

 that both the filling of the old river-beds, and their protection by lava, 

 took place comparatively rapidly, and were together the closing scene 

 of the Tertiary drama. The deep gravels, therefore, may be placed 

 indifferently in the latest Pliocene or earliest Quaternary. The newer 

 gravels are undoubtedly Quaternary and recent. Certain it is that the 

 deep placer-gravels are similar in all respects to the Quaternary gravels 

 all over the world, except that, by percolating alkaline waters contain- 

 ing silica, they have been cemented in some cases into grits and con- 

 glomerates. This is because they are covered with lava which 3 T ields 

 both the alkali and the soluble silica, as already explained (p. 248). 



In any case, we have here an admirable illustration of the immen- 

 sity of geological times. The whole work of cutting the hard slate- 

 rock 2,000 feet or more has been done since the lava-flow, and therefore 

 certainly since the beginning of the Quaternary. But it is necessary 

 to remember that, on account of the high slope of the new river-beds, 

 the work was exceptionally rapid. 



CHAPTER VI. 

 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 



Characteristics. — The Quaternary, and, indeed, all previous ages, 

 were reigns of brute force and animal ferocity. A condition of things 

 prevailed which was inconsistent with the supremacy of man. The age 

 of man, on the contrary, is characterized by the reign of mind. There- 

 fore, as was necessary, the dangerous animals decreased in size and 

 number, and the useful animals and plants were introduced, or else 

 preserved by man. 



Distinctness of this Era. — In regard to the distinctness and impor- 

 tance of this era, there are two views which will probably ever divide 

 geologists, depending on the two views regarding the relation of man 

 to Nature. From the purely structural and animal point of view, man 

 is very closely united with the animal kingdom. He has no department 

 of his own, but belongs to the vertebrate department, along with quad- 

 rupeds, birds, reptiles, and fishes. He has no class of his own, but be- 



