Ransome.] The Great Valley. 385 



while to the south of the 40th parallel the probabilities are that the 

 sea had an almost, or wholly, unbroken sweep across the area now 

 occupied by the Coast Ranges and the Great Valley. 



"The Miocene," says Mr. Diller, "was initiated with no marked 

 change of level in Northern California unless a subsidence."* The 

 great development of marine Miocene throughout the Coast Ranges, 

 and its occurrence on the west slope of the Sierra Nevada at Ocoya 

 Creek, f and also at the Marysville Buttes,J would indicate that the 

 sea had free access to the Sierra Nevada across the site of the Coast 

 Ranges, and over the greater part of the area now occupied by the 

 Great Valley. On the other hand, the brackish-water character 

 of the (supposedly Miocene) lone formation would indicate the 

 existence of some barrier between the northern and middle por- 

 tions of the Sierra, and the open sea to the west. Of course if the 

 peneplain described by Mr. Diller be of Miocene age, then there 

 was a very definite land barrier to the west of the present upper 

 Sacramento Valley; but it seems almost incredible that, during the 

 folding and elevation of the great Miocene sediments throughout 

 the Coast Ranges, and the upheaval of the Klammath Mountains by 

 several thousands of feet, that a strip of peneplain should still be 

 preserved about the western borders of the upper Sacramento Val- 

 ley, which has suffered little change beyond being gashed by the 

 canons of the modern streams, and is still an easily-recognized 

 feature in the topography. 



Lastly, the age of the brackish-water lone formation is still a 

 somewhat unsettled question, and this should be borne in mind 

 when drawing conclusions as to the physical geography during 

 Miocene times. It is possible that with further knowledge of the 

 mountain ranges inclosing the Great Valley we may be able to 

 trace in Miocene times the first faint boundaries of the whole 

 or a part of the valley as known to us to-day, but at the present 

 time we must agree substantially with AntisellS in considering that 

 " probably during the whole of the Miocene the Coast Range was 



* Loc. cit. 



t Blake, Pac R. R. Reports, Vol. V, Geology, p. 164. Also Whitney, 

 Geol. of Calif., p. 201. 



{Marysville Folio, U. S. Geol. Survey. 



^Pacific R. R. Reports, Vol. VII, Geology, p. 19. 



