Befteubeb 10, 1909] 



SCIENCE 



349 



about the middle of the Miocene, and the 

 Coast Range disturbance was probably a local 

 phase of the same revolution. 



In the upper Miocene the climate was no 

 longer subtropical, but warm-temperate and 

 moist, like that of the states bordering the 

 present Gulf of Mexico. Marine animals like 

 those of our time abounded in the waters, but 

 along with them were some southern forms. 

 And on the land elms, walnuts, hickories and 

 laurels flourished, indicating a temperate, 

 rainy climate, moister if not milder than that 

 of to-day in the same region. 



In the Sierra Nevada in this epoch there 

 were large rivers, not running swiftly in deep 

 canyons, as they do now, but winding slowly 

 down low grades, overloaded with sediments, 

 the auriferous gravels. These dead rivers, 

 which must have run on a low plain not far 

 above sea-level, are now found high up in the 

 Sierra Nevada, with their channels buried 

 deeply under later lava flows, and warped by 

 later erogenic movements. 



In the Pliocene the warm-temperate types 

 of plants have disappeared temporarily, and 

 the salt-water faunas, too, show a change for 

 the worse. The fresh-water Pliocene lake 

 beds also show the influence of a cooler cli- 

 mate, for while many of the fossil mollusca 

 are the same as species now existing in that 

 region, others that are still living are now 

 found only in the Klamath Mountains. 



Now the land had begun to encroach on the 

 sea, and the shore was receding westward. 

 The whole west coast was rising, and the salt 

 waters no longer reached to the foot of the 

 Sierra Nevada, nor even to the great valley. 

 But the elevation was not uniform, for valleys 

 in the Coast Ranges that had been cut during 

 the Miocene were filled with sediments during 

 the Pliocene, which was made possible by 

 local subsidence along the coast. The im- 

 mense deposits of the Great Valley belong 

 partly to this epoch, and partly to the Quater- 

 nary, but they are wholly of fluviatile origin. 

 These gravels and silts have been bored into 

 to the depth of three thousand feet in the 

 middle of the Great Valley, and still bed-rock 

 was not reached. 



During the Pliocene the Sierra Nevada was 

 elevated again, and the rejuvenation of the 

 streams carried the sediments out of the 

 mountains to the flats of the valley floor, 

 piling up the gravels and clays now known as 

 the Tulare formation. California of that 

 time was very much like California of to-day, 

 with a great mountain range on the east; in 

 the middle a long, broad valley, low-lying, and 

 covered in many places by fresh- water lakes; 

 and on the west, a long, low, narrow mountain 

 range. On the submerged narrow coastal 

 plain, and in troughs parallel to this range, 

 were laid down the marine Pliocene sediments. 



About the close of the Pliocene, and in early 

 Quaternary, the elevation of the west coast 

 continued, causing deep canyons to be exca- 

 vated by the vigorous streams, in the Sierra 

 Nevada, and in the Coast Ranges. This epoch 

 has been called by Professor Le Conte the 

 Sierran epoch. The results of this erosion are 

 still seen in the deep canyons, the most stri- 

 king scenic features of the Sierra Nevada, 

 but those of the Coast Ranges are now seen 

 only on hydrographic charts, for they are now 

 buried two or three thousand feet under the 

 ocean. This shows that in early Quaternary 

 time the coast stood two or three thousand feet 

 higher than now. The record of that time is 

 purely one of events, for the sediments that 

 were laid down in the bordering sea are now 

 covered by the ocean, and the region that is 

 now above sea-level stood too high for much 

 deposition. The Sierran epoch corresponds to 

 the pre-Glacial or Ozarkian epoch of the east- 

 ern states. 



Increasing cold accompanied the period of 

 elevation, and this culminated in the Glacial 

 Epoch, in which the Sierra Nevada was cov- 

 ered by a continuous sheet of ice. The ice 

 made its way down sheltering canyons to 

 places that are now 3,500 feet above sea-level, 

 but which then stood several thousand feet 

 higher. This means that in the Glacial 

 Epoch the climate of California was very 

 similar to that which now prevails on the 

 Olympic Peninsula in Washington, for in that 

 region glaciers still come down to 6,000 feet 

 above the sea, the climate is cool and rainy, 



