562 CENOZOIC ERA— AGE OF MAMMALS. 



by sedimentation lias continued up to the present moment, and the 

 deposit (river-swamp and delta deposit) has reached, according to 

 Hilgard, a thickness of fifty to a hundred feet. Thus the phen- 

 omena of the Mississippi distinctly separate the Terrace from the Re- 

 cent epoch. 



Quaternary Period on the Western Side of the Continent. 



All the most characteristic phenomena of this period, such as old 

 sea-margins, general glaciation, flooded lakes, and old river-beds, are 

 abundant and conspicuous on the western side of the continent. As 

 it is impossible to synchronize perfectly these phenomena with those 

 already described on the eastern side, it will be best to take them in the 

 order named above and trace each kind through the whole period. 



1. Sea. — The phenomena along the sea-coast show both elevation 

 and depression. A more elevated condition than the present is shown 

 by the bold, rocky coast and high island standing a little way off the 

 coast. The islands off the coast of the southern part of California, and 

 separated from the mainland by the Santa Barbara Channel, are evi- 

 dently continental islands. They were undoubtedly a part of the con- 

 tinent during the late Tertiary and early Quaternary times, and were 

 separated subsequently by subsidence. This is clearly shown by their 

 flora,* and especially by the remains of the Mammoth on one of them 

 — Santa Rosa.f Another very striking proof of continental elevation 

 is found on this, as on the Eastern coast, in the existence of deep sub- 

 marine channels cutting through the submerged continental plateau, 

 and evidently produced by subaerial erosion during late Tertiary times. 

 I am indebted to Prof. Davidson for facts, yet unpublished, concerning 

 these. There are about twenty of these off the California coast, nine 

 or ten of which are very marked. Commencing at Cape Mendocino, 

 and going southward, four very deep ones are found in 25 miles — one, 

 very marked, in the Bay of Monterey, one in Carmel Bay, one off the 

 eastern entrance of Santa Barbara Channel, two in the Bay of Santa 

 Monica, and one off the harbor of San Diego. These channels show a 

 previous elevation of 2,500 to 3,000 feet. Bat there is one peculiarity 

 of these as compared with those on the Eastern coast, viz., that they 

 do not, in any evident way, correspond to the mouths of the present 

 rivers, but, on the contrary, often abut against a bold coast, rising to 

 3,000 feet within three miles of shore. The explanation of this differ- 

 ence is found in the enormous orographic changes which occurred 

 on this coast in early Quaternary times. Of this we will speak again. 



* American Journal of Science, vol. xxxiv, p. 457, 1887. 



f Proceedings of the California Academy of Science, vol. v, p. 152. The remains of 

 two more elephants were found on Santa Rosa, in October, 1890, by Mr. C. D. Voy. 



