University of California. 



[Vol. i. 



deposits. They are all of distinctly fluviatile, or possibly shallow- 

 lacustrine character, and indicate a rather - gradual and gentle sub- 

 sidence, with no marks of the catastrophic downward plunges of 

 the crust required by the theory of isostasy when pushed (as above) 

 to its logical conclusion. 



In the Sacramento Valley, Diller has described some features 

 which do not seem to be in full accord with the hypothesis of 

 isostatic subsidence. About five miles east of the Sacramento 

 River, at Red Bluff, the bed of Tuscan tuff is described as bending 

 abruptly downward toward the west, beneath the newer formations 

 of the valley.* The same tuff exposed in Iron Canon, five miles 

 north of Red Bluff, exhibits a well-defined transverse, or east and 

 west, anticlinal arch, which is also well shown in the railroad levels 

 in the valley. f These flexures of the younger deposits in the 

 Great Valley, although they occur too close to its margin to be 

 of the highest value as evidence, yet, as far as they go, seem to 

 indicate that the valley floor is subjected to a compressive stress, 

 whereas, in accordance with the isostatic hypothesis, it should be 

 under 'tension; the tendency should be to smooth out all existing 

 minor wrinkles, rather than to create new ones. 



The same writer refers to a local subsidence at Cherokee Flat, 

 on the eastern border of the Sacramento Valley, whereby "the finer 

 essentially estuarine deposits over 300 feet in thickness, lap over to 

 the eastward upon the ancient river and shore gravels mined at 

 that place." J This local subsidence must have taken place, or at 

 least begun, before the accumulation of any of the finer sediments, 

 and indicates a local movement independent of loading; for as river 

 and shore gravels are formed at or above the local baselevel, sub- 

 sidence must have taken place before finer estuarine deposits could 

 be laid down upon them. 



Becker, § Ross Browne, || and Lindgren \ have all called atten- 



* Loc. r/7., p. 414, also 8th An. Rept. U. S. Geol. Survey, p. 425. 

 t Loc. cit., p. 433. 

 X Loc. cit., p. 428. 



\ Structure of a Portion of the Sierra Nev., Bull. Geol. Soc Am., Vol. II, 

 pp. 49-74 



|| Ancient River Beds of Forest Hill Divide, 10th An. Rept. State Mineral- 

 ogist of Cali r ., p. 443. 



1f Two Neocene Rivers of Calif, Bull. Geol. Soc. Am., Vol. IV, pp. 297, 298. 



