THE TERTIARY LAKE BASIN AT FLORISSANT, COLO., BETWEEN 
SOUTH AND HAYDEN PARKS.,* 
[With a map. ] 
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. C. 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 up in the 
mountains at the southern extremity of the Front Rarge 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 bis account of the geology of Hayden Park and the country 
lying between it and the upper cafion of the South Platte.t 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 cafion. ‘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 blutts 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 
are more or less argillaceous, and containing fragments and stems of 
leaves. 
“3. Coarse gray and yellow sandstone. 
“4, Chocolate-colored clay shales with fossil leaves. At the upper 
part these shales are black, and below pass into— 
“5. Whitish clay shales. 
“These last form the base of the hill. The beds are all horizontal. 
“Reprinted with additions and alterations from the Bulletin of Survey, vol. vi, art. 
Hs 
t Ann. Rep. U. S. Geol. Sury. Terr. 1873, p. 210. 8vo. Washington, 1874. 
271 
