THE SANDSTONE OF FOSSIL RIDGE 185 
Baculites ovatus, Inoceramus barabini and Avicula linguiformis have 
been reported to range through the Pierre and into the Fox Hills. 
The following are in other localities usually confined to upper Pierre 
or Fox Hills, or both, and have not been found in or immediately above 
the Hygiene at Boulder: 
Ostrea pellucida Margarita nebrascensis 
Volsella meekit Anchura americana 
Thracia gracilis Anisomyon patellijormis 
Scaphites nicolletii 
The following, though we have found them elsewhere in northern 
Colorado only in Upper Pierre and Fox Hills strata, are known in other 
regions to range low in the Pierre, according to Dr. T. W. Stanton (MSS): 
Avicula nebrascana Pholodomya subventricosa 
Cardium speciosum Tellina scitula 
Placenticeras intercalare 
From the foregoing it seems clear that the fauna itself is not deter- 
minative of the exact horizon, so that we must rely upon the stratigraphic 
evidence. 
Professor D. W. Spangler, Messrs. G. S. Dodds, Harvey C. Markman 
and Harry W. Clatworthy have rendered notable assistance in this work, 
particularly in the search for fossils. The writer also wishes to express 
appreciation of the great assistance rendered by Dr. T. W. Stanton, of 
the United States Geological Survey, in the identification of material 
and in advice on various matters, and the assistance of Professor R. P. 
Whitfield in identifying a few specimens. Descriptions are in prepara- 
tion of several new species found at Fossil Ridge. 
PARTIAL BIBLIOGRAPHY 
The following works bear either directly upon the sandstones in ques- 
tion or contain descriptions, figures or discussions of species found at 
Fossil Ridge: 
Cross, WHITMAN. See Emmons. 
ELDRIDGE, GEORGE H. See Emmons. 
Emmons, SAMUEL F., WHITMAN CROSS AND GEORGE H. ELDRIDGE. Geology of the 
Denver Basin. U.S. Geol Sur., Mon., Vol. XXVII, 1896. Discusses the Cretaceous 
formations in detail, mentions sandstone probably same as Hygiene and contains 
list of fossils on pp. 78, 79. 
