Art. XI.— The Tertiary liake-basin at Florissant, Col- 

 orado, betiveeii S^otith and Mayden Parks. 



By Samuel H. Scudder. 



The following remarks are based upon collections and notes made 

 during a visit to Florissant in the summer of 1877 in company with 

 Messrs. Arthur Lakes, of Golden, Colo., and F. 0. Bowditch, of Boston, 

 Mass. As five days only were spent in the place, most of the time was 

 given up to the collection and care of specimens, so that only a general 

 survey of the locality was possible. Mr. Lakes especially gave himself 

 to the study of the geology of the district, and as he was previously 

 familiar with the structure of the surrounding country and placed his 

 notes at my disposal, the first part of this paper should be considered 

 our joint production. 



GEOLOGY. 



The tertiary lake-basin at Florissant, already famous for its prolific 

 beds of plants and insects, is situated in a narrow valley high u}) in the 

 mountains at the southern extremity of the Front Range of Colorado, at 

 no great distance from Pike's Peak. The first, and so far as I am aware 

 the only notice of it which has been published, is that by Mr. A. C. 

 Peale in his account of the geology of Hayden Park and the country 

 lying between it and the upper canon of the South Platte.* As it is 

 brief, it is given here in full : 



" The latter [Beaver Creek] flows to the northwest, and empties into 

 the South Platte just below the upper caiion. About five miles from its 

 mouth, around the settlement of Florissant, is an irregular basin filled 

 with modern lake deposits. The entire basin is not more than five miles 

 in diameter. The deposits extend up the branches of the creek, which 

 all unite near Florissant. Between the branches are granite islands 

 appearing above the beds, which themselves rest on the granite. Just 

 below Florissant, on the north side of the road, are bluffs not over 50 

 feet in height, in which are good exposures of the various beds. The 

 following section gives them from the top downward : 



"■ 1. Coarse conglomeritic sandstone. 



"2. Fine-grained, soft, yellowish white sandstone, with bands that 



* Anu. Rep. U. S. Geol. Sivrv. Terr. 1873, p. 210. 8vo. "WasbiDgtou. 1874. 



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