THE EOCENE PERIOD 797 



Climate. The marine fauna of the Pacific coast, 1 and the flora 2 

 as far north as Puget Sound, point to a subtropical climate. 



THE OLIGOCENE FORMATIONS 



In North America. As already stated, formations correspond- 

 ing to the Oligocene of Europe have not usually been differentiated, 

 in North America. The differentiation may be justified on paleon- 

 tological grounds, if it is desirable to make the classification for this 

 country conform closely to that of Europe. 3 If the Oligocene is 

 to be recognized, certain formations along the Atlantic and Gulf 

 joasts, formerly regarded as late Eocene or early Miocene, should 

 )e classed as Oligocene. In the Gulf region the Vicksburg (below) 

 ind Grand Gulf formations 4 of Alabama, Mississippi, and Louisiana, 

 ind the Fayette 5 formation of Texas, belong to this category. 



The early Oligocene is represented generously about the Carib- 

 bean sea, where its association with the Eocene is generally close, 6 

 ind its separation from the Miocene distinct. This is in keeping 

 svith the phenomena of the Gulf States. Limestone is the dominant 

 ype of rock in the Antillean region. 



The Oligocene stage is also recognized among the terrestrial 

 deposits of the western part of the continent. The White River 

 ? ormation, now classed as Oligocene, occupies an extensive area in 

 northeastern Colorado, southwestern Wyoming, western Nebraska 

 (Brule and Chadron formations 7 ), and South Dakota, and perhaps 



Arnold, Jour. GeoL, 1909. 



2 Knowlton, Tacoma, Wash. Folio. 



3 For table of Oligocene formations, see Dall, 18th Ann. Kept., U. S. Geol. 

 Surv., Pt. II. 



4 The classification of the Grand Gulf formation is in dispute. Some of 

 the beds described under this name are probably younger than Oligocene; 

 see Smith and Aldrich, Science, N. S., Vol. XVI, p. 836, and Vol. XVIII, p. 26. 



5 Penrose, Geol. Surv. of Texas, 1st Ann. Kept. 



8 Hill, Geology and Physical Geography of Jamaica, and Geological His- 

 tory of the Isthmus of Panama and portions of Costa Rica. Bull. Mus. Comp. 

 Zool., Vols. XXVIII and XXXIV respectively. 



7 Barton, Camp Clarke, Scotts Bluff, Edgemont, and Oelrichs folios, U. 

 p. Geol. Surv. 



Meyer; o and p, Protocardia levis Conrad; q, Ostrea compressirostra Say; 

 r, Modiolus alabamensis Aldrich; s, Lucina aquiana Clark; t, Leda parilis 

 (Conrad); u, Crassatellites alceformis (Conrad); v, Nucula ovula Lea; w t 

 Pecten choctawen&is Aldrich. (Maryland Geol. Surv.) 



