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Geology of Castle Rock.—Lee. 99 
in the Castle Rock region. They are the wide spread and well 
known formations of the western interior and may be passed 
over at present with little comment. Their general distribu- 
tion is perhaps sufficiently indicated by the accompanying map. 
The sandstones and conglomerates of Perry park, which have 
just been described, lie at an inclination of something like ten 
degrees. As already shown, it is doubtful how much of this 
series belongs to the formation commonly known as Trias. 
There is, however, a group of nearly veriical red strata east of 
the park forming the wall which divides the park from the 
plains region to the east. There is no doubt that this ver- 
tical series is a part of what is here referred to as the Red Beds 
proper. Near the top of this series in Perry park occurs a 
heavy bed of gypsum. It outcrops for a distance of about 
eight miles, and attains a thickness in places of fifty to seventy- 
five feet. It is not found beyond the limits of the park. 
The thickness of the gypsum varies within short distances, the 
variation being due in some cases at least to a local thinning 
from bottom upward. 
Fossils were found in the Morrison, Benton, Niobrara, and 
Ft. Pierre. The Morrison yields dinosaurs, but only fragments 
have thus far been excavated. A small collection of inverte- 
brates from the Benton near Deadman creek south of the 
southern border of the area mapped contained the following 
species.* 
Ostrea congesta var. bentonensis, Inoceramus platinus, 
Inoceramus gilberti, Prionocyclus wyomingensis, 
< labiatus, Baculites sp. 
The Niobrara limestone contains great numbers of Jnocera- 
mus deformis. The lower member of this limestone in Perry 
park is a tough brown stratum composed principally of frag- 
mentary shells. Among these, Ostrea congesta var. mobrar- 
ensis and Inoceramus pinnatus were recognized. A number of 
shark’s teeth were ?lso found. The Ft. Pierre of Perry park 
yielded the following: 
Lucina occidentalis Baculites ovatus 
Inoceramus barbini Ammonities sp. 
These forms occur in masses of shell limestone which re- 
semble the “teepe buttes” of central and eastern Colorado.+ 
*These and the following Mesozoic forms were identified by Dr. W.N LoGan. 
#G. K, GiLpert, U.S Geol. Surv., 17th Ann, Rep. “Underground Waters 
af the Arkansas.” 
