184 UNIVERSITY OF COLORADO STUDIES 
broken. Quiet water is also indicated by absence of cross-bedding and 
coarse material. 
While it may be true that the two sandstones are not absolutely syn- 
chronous, on the whole it seems quite probable that they are. The two 
seem to occupy the same positions with reference to the overlying Fox 
Hills sandstones and the underlying Niobrara limestone. The. fauna 
of the Fossil Ridge district bears a much closer resemblance to that of 
the Fox Hills formation than does that of the Hygiene horizon at Boulder, 
but the absence of many of the Fox Hills species from the Boulder 
District may be due to local conditions existing during Pierre 
time, though more likely the apparent difference is due to the less 
fossiliferous character of the outcrops in the Boulder District. The 
paleontologic evidence is not sufficient to overcome the direct 
stratigraphic evidence. 
ANALYSIS OF FossiIL RIDGE FAUNA 
The following species have almost no value in this connection, for 
various reasons, many of them being found in only one or two localities 
and consequently their geological range being but little known: 
Beaumontia solitaria Capulus n. sp. 
Chetetes dimissus Gyrodes crenata 
Serpula n. sp. Anchura haydent 
Panopea berthoudi Volutoderma n. sp. 
Ostrea patina Anisomyon centrate 
Anatina n. sp. 
Halymenites major is said to range as low as the Benton and is 
common in the Fox Hills sandstone, so that it is without value in this 
discussion. 
Baculites compressus and Scaphites nodosus have been found just 
below the Hygiene at Boulder. 
The following have been found immediately above the Hygiene at 
Boulder: 
Inoceramus oblongus Callista deweyt 
Inoceramus proximus Anisomyon borealis 
Inoceramus vanuxemt Nautilus dekayi 
Ostrea inornata Placenticeras whitfieldi 
Anomia retiformis 
