THE SANDSTONE OF FOSSIL RIDGE 181 
The importance of a thorough understanding of the Cretaceous 
sandstones in connection with irrigation projects and the utilization of 
the high, dry plains is also becoming more and more apparent. These 
sandstones absorb great quantities of water from ditches and reservoirs, 
carrying it off beneath the surface, to reach the surface again perhaps 
far away from the point of entrance. As the demand for water for 
irrigation increases the necessity of stopping this seepage by avoiding 
the sandstones or cementing over them will increase. On the other 
hand, experience proves that a thorough knowledge of these sandstones 
and their relations to overlying and underlying formations will greatly 
simplify the problem of wells for minor irrigation and stock watering 
on the divides which cannot practically be reached by ditches from 
streams. 
This paper is not intended as a complete solution of any of these 
problems, but merely to record at least a portion of our present knowledge 
of an important member of the Pierre Group, which may be of assistance 
to future workers in the field. 
Emmons, Cross and Eldridge long ago reported a persistent sand- 
stone in the lower Pierre of the Denver Basin. More recently Dr. Fen- 
neman described more in detail a sandstone in the lower Pierre of the 
Boulder District, which he called the Hygiene, extending from the 
northern part of the area covered by the Denver Basin monograph 
to a point west of Berthoud, which is likely a continuation of the one 
in the Denver Basin. Early in our work upon Fossil Ridge the writer 
was impressed with the possibility that it was a continuation of the Hygi- 
ene sandstone. Against this idea were two facts, the distance of Fossil 
Ridge from the foothills and the presence therein of numbers of Fox 
Hills species which are not found in the Pierre of the Boulder District. 
The first objection is explained away by our investigations, but the other 
is still unexplained. The Niobrara formation is found quite uniformly 
at the base of the first slope of the foothills. By referring to the map 
herewith it will be noted that the Hygiene at Boulder is within one-fifth 
of a mile of the Niobrara outcrop, while nine miles farther north it is 
about two miles distant with a dip of 63 degrees. Opposite the Rabbit 
Mountain fold east of Lyons we found it again within one-half mile of 
