September 10, 1009] 



SCIENCE 



347 



omitted. The Pacific Ocean still washes the 

 western shore of California, now encroaching, 

 and now retreating; but the Great Basin Sea 

 is long since dead, and would be buried, were 

 it not for the later uplifts that rear its old 

 sediments in the mount^n ranges of the 

 desert region. 



In early Cambrian time sedimentation be- 

 gan in the eastern part of California on the 

 western shores of the Great Basin Sea, and 

 kept up, almost without interruption, until 

 the middle of tbe Jurassic. During this long 

 period the greater part of the state appears to 

 Lave been above water, although during the 

 Santa Lucia epoch (Paleozoic?), calcareous 

 sediments were laid down in the Coast Ranges, 

 and during the Carboniferous the Great Basin 

 Sea spread westward and southward over 

 much of the region of the Sierra Nevada. 

 In the Permo-Carboniferous, California, al- 

 though remote from the center of activity, 

 felt the effects of the Appalachian revolution, 

 for an uplift began along the axis of the 

 Sierra Nevada, manifesting itself in great out- 

 pourings of volcanic tufis, which now are 

 preserved as greenstones, showing by their 

 marine fossils that they were deposited in the 

 sea. Further west, the calcareous sediments 

 of the Santa Lucia Mountains were raised 

 above the sea and changed into marbles and 

 schists. 



The Appalachian revolution restricted, but 

 ■did not obliterate, the Great Basin Sea, nor 

 did it confine the relentless advance of the 

 Pacific Ocean, for during the Jurassic marine 

 sediments were laid down along the Coast 

 Hanges, and along the sides of the Sierra. 

 The Franciscan series has presented this 

 record in the Coast Ranges, and the Mariposa 

 formation in eastern California. 



The Cordilleran revolution began in the 

 ■Great Basin Sea in the middle of the Jurassic, 

 when that body of water, after many vicissi- 

 tudes, finally went dry, and has never since 

 "been covered by salt water, although in later 

 ages Tertiary and Quaternary lakes have been 

 scattered over its dead basin. 



This elevation culminated, in late Jurassic 

 time, in the upturning and metamorphism of 



the Triassic and Jurassic sediments of the 

 Sierra Nevada, and the Franciscan beds of 

 the Coast Ranges. Since that time the Sierra 

 Nevada has been above the sea, subjected to 

 continuous erosion, and there we see the deeper 

 results of metamorphism. The Coast Ranges, 

 on the other hand, have been buried under the 

 later Cretaceous and Tertiary sediments, and 

 the deeper products of metamorphism are 

 little exposed. The glaucophane schists of 

 the Coast Ranges are evidences of rather 

 shallow hydrothermal metamorphism, while 

 the great masses of thoroughly altered rocks 

 and auriferous veins of the Sierra Nevada 

 show the deep-seated action in that region. 

 This explains the fundamental difference be- 

 tween the metamorphic rocks of the two areas, 

 where the phenomenon was contemporaneous, 

 and the rocks affected were similar in the be- 

 ginning. 



During this epoch along the western coast, 

 from Oregon to Lower California, there was 

 much igneous activity, and great masses of 

 serpentine are now seen throughout the Coast 

 Ranges, the results of alteration of the perido- 

 tite dykes that were intruded into the Francis- 

 can sediments. 



It is probable, also, that the Cordilleran 

 revolution was something more than a mere 

 orogenic disturbance, for it marks a change 

 from the warmth of the Middle Jurassic, with 

 its cyeads and reef-building corals, to the 

 cooler epoch of the Upper Jurassic, with its 

 scanty boreal fauna. The Middle Jurassic 

 was of tropical type, from Mexico to Alaska, 

 and uniform up to Franz Joseph Land. 

 The Upper Jurassic, on the other hand, was 

 of Boreal type from the Arctic Region down 

 as far as California, and for a short epoch in 

 the Portland these conditions extended down 

 as far as Mexico. 



After this moimtain-making epoch near the 

 close of the Jurassic, the sea again encroached 

 on the uplifted area, and the Knoxville sedi- 

 ments were laid down on the western border of 

 the Coast Ranges. The lower Knoxville beds 

 contain a fauna closely related to that of the 

 ^fariposa, still with Jurassic types of Aucella, 

 and with the same poverty of other animals. 



