OF THE WEST COAST 



308 



considerable maonitiKk' s("|)aratinK tlie two epocliH of deposition. This 

 assumption is borne out by the fact that we find, especially in the eastern 

 Coast Eanges, evidences of a marked unconformity between the San 

 Lorenzo and the Monterey. The Kreyenhagen shales, which are of San 

 Lorenzo age, were here folded and the folds cut off before the deposition 

 of the Monterey or Vaqueros sediments on their upturned edges. See 

 note on the Kreyenhagen shales at bottom of page 299. 



Distribution of Oligocfne ix Oregon and Washington ^ 



The condition of de})osition in Oregon and Washington during Oligo- 

 cene time was similar to that which existed during the same period in 

 California. These beds were deposited in geosynclinal depressions par- 

 tially inclosed by land. It seems very probable that there w^as one large 

 trough, which extended between the western front of the Cascades and the 

 Olympics, connecting with the ocean to the north })etween a land-mass, a 

 part of which is now Vancouver Island, and the area now including the 

 Olympic Mountains, and to the south in the region of the Columbia 

 River. The greatest amount of folding of the beds, which were deposited 

 in this trough, has been iji the region of Puget Sound, where is found the 

 greatest thickness of Oligocene sediments — a thickness of over 10,000 

 feet. 



Fauna and climatic Conditions of Oligocene 



general observations 



The fauna of the West Coast marine Oligocene is as yet only partially 

 described. At the present time more than 200 species are known from 



^ Our present knowledge of the stratigraphy and faunas of the Oligocene of Oregon, 

 Washington, and Vancouver Island is due, to a large extent, to the work of Ralph 

 Arnold, Harold Hannibal, and C. E. Weaver. It was largely through the field-work of 

 Hannibal during the years of 1911 and 1912 that the stratigraphic sequence, now for 

 the most part generally accepted, was first established. The Oligocene-Miocene sequence, 

 as recognized by Arnold and Hannibal in their paper, "The marine Tertiary stratigraphy 

 of the north Pacific Coast of America." Proc. Amer. Philos. Soc, vol. 52, 1913, pp. 573- 

 589, was, beginning at the base : 



1. The Sooke formation. 



2. The San Lorenzo formation. 



3. The Seattle formation. 



4. The Twin River formation. 



5. The Monterey formation. 



We now know, due to the discovery of a vertebrate fauna in the Monterey of Coalinga 

 region (.1.' C. Merriani : Tertiary vertebrate faunas of the north Coalinga region of Cali- 

 fornia, Amer. I'hilos. Soc. n. s., vol. xxii, pt. 3. 1915, pp. 21-2G), that this epoch of 

 deposition extended into the middle Miocene, and it seems more than probable that the 

 lowest Vaqueros beds are not older than l^ower Miocene. 



For map showing distribution of Oligocene deposits in Washington, see paper by C. E. 

 Weaver : "Tertiary formations of western Washington," Wash. State Geol. Surv. Bull. 

 13, 1910. pp. 13-271. 



