182 UNIVERSITY OF COLORADO STUDIES 
the Niobrara with a dip of 70 degrees. This difference in relative posi- 
tion is due chiefly to folds and difference in dip, though possibly there 
is also some difference in the thickness of the underlying portion of the 
Pierre shales, as it would not be likely to retain the same exact thickness 
for such distances. From the Rabbit Mountain outcrop the sandstone 
continues northward with a dip of about 15 degrees, exposed at intervals 
about a mile from the Niobrara outcrop, to a point west of Berthoud 
whence it is thrown rapidly to the eastward in its northward extension, 
the sudden change in strike being due chiefly to a change in direction of 
dip produced by the Arkins fold. At the same time the distance from 
the foothills increases to an average of nearly three miles, largely in 
consequence of the flattening of the dip, which in places from Loveland 
northward falls as low as eight degrees and north of Ft. Collins drops 
to five degrees. The sandstone passes into the Big Thompson Valley 
about half a mile southeast of Loveland and is covered by river débris, 
but outcrops again on the north side of the valley immediately northeast 
of town at the south end of Lake Loveland, there occupying almost exactly 
the same relative position with reference to the Niobrara as at Fossil 
Ridge, and containing numbers of Inoceramus oblongus, Anomia reti- 
formis and Scaphites nodosus, so characteristic of Fossil Ridge. We 
found there, too, a tendency toward concretionary structure of the 
sandstone, though not so pronounced as at Fossil Ridge. From this 
point the sandstone is traceable directly into Fossil Ridge, leaving little 
chance for doubt that Fossil Ridge is a tontinuation of the Hygiene 
sandstone. We have not traced the sandstone across the Cache la 
Poudre Valley, but from where it disappears on the south side of the valley 
we passed northward through Ft. Collins and found it exactly where 
it should occur on the north side-of the valley, in every respect the same 
as at Fossil Ridge, including the typical concretions and their fossils. 
From Loveland northward the strike is almost due north as far as we 
traced it. North of Ft. Collins it passes along the east shores of Terry 
Lake, Rocky Ridge Reservoir No. 1 and Douglas Lake Reservoir No. 10; 
the cutting away of the sandstone at the two latter places by undermining 
from the west forms a steep west-facing bluff which slopes from the 
escarpment gently eastward. This is called Rocky Ridge. While the 
