798 GEOLOGY 



m Kansas. 1 In the light of present knowledge, it seems prob;d>lo 

 that all phases of land aggradation, lucustrine, fluvial, and rohan, 

 are represented in this formation. 2 Even thin beds and leu 

 limestone and volcanic ash enter into it. The formation is said to 

 have originally covered most of the Black Hills region, and possibly 

 all of it. 3 Remnants are now found up to elevations of more than 

 6,000 feet, and the highest points of the hills are but little higher. 

 The Florissant beds in South Park, Colo., consisting largely of 



Fig. 536. Chimney Rock, a detail in the Bad Lands of the Whit.- 

 country. The base of the column is Brule clay. (Darton, U. IS. ' 

 Surv.) 



volcanic ash, and famous for their extraordinary number oi 

 insects, are classed as Oligocene. So also are some of the bods <>i 

 the John Day Basin of Oregon, 4 unconformable above tho Korono. 

 Marine Oligocene beds are found in California, Oregon, Washing- 

 ton, British Columbia, and Alaska, at least, 5 but at many point.- 

 on the Pacific coast, the record of the period is found chiefly in tin- 

 uncomformity between the Eocene and the Miocene. Tho land- 



1 Adams, Am. GeoL, Vol. XXIX, p. 303. 



2 Fraas, Science, Vol. XIV, N. S., p. 212, and Matthew. Am 

 XXXIII, p. 403, 1899. 



3 Darton, 19th Ann. Kept., U. S. Geol. Surv., Pt. IV; 21st Ann ! 

 U. S. Geol. Surv., II. 



4 Dall, 19th Ann. Kept., U. S. Geol. Surv.; Merriam, Jour. ( Jml., Vol. 1 

 pp. 71-72, and Bull. Univ. of Cal., Vol. II, pp. 270 et seq. 



5 Arnold, Bull. 321, U. S. Geol. Surv. 



