THE SANDSTONE OF FOSSIL RIDGE IN NORTH- 
ERN COLORADO AND ITS FAUNA 
By Junius HENDERSON 
Fossil Ridge is a low ridge of sandstone extending in an approximate 
north-south direction for several miles, lying between the Colorado and 
Southern Railway track and the Ft. Collins-Loveland wagon road, 
south of Ft. Collins. Fossil Creek cuts through the ridge about five 
miles south of Ft. Collins, near where the ridge in its northward extension 
passes into the general level of the divide and thus disappears. Weath- 
ered out on the surface of this sandstone are innumerable hard, sandy 
concretions, from a few inches to four feet in diameter, containing large 
numbers of fossils, which have given to the ridge and creek the names 
they bear. The large size and abundance of some of the species attract 
the attention of even the most unobserving traveller who passes over 
the ridge. In the early reports the locality was variously called Fossil 
Ridge and Fossil Creek. As the ridge follows a definite stratigraphic 
horizon, while the creek cuts across strata several thousand feet in thick- 
ness, the former name seems preferable in a geological sense. 
This vicinity is of peculiar interest to the paleontologist as the type 
locality of some interesting forms, as well as because of the pronounced 
intermingling of Pierre and Fox Hills species. A correct understanding 
of this and related sandstones may also have a very practical value in 
the exploration for oil. 
These beds seem to occupy a position about one-third of the way 
up from the bottom of the Ft. Pierre Cretaceous. As the Pierre in this 
region is from 5,000 to 7,000 feet in thickness, the importance of finding 
narrow, persistent, identifiable horizons, either lithological or paleon- 
tological, within the formation, is at once apparent. Oil of excellent 
quality and in paying quantities is found in the Pierre at several places 
in Colorado, as at Boulder and Florence. There is every reason to 
believe that the production of petroleum may be greatly increased by 
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