STRUCTURAL FEATURES IN THE FOOT-HILL REGION. 251 
along the mountains the above topographical features may 
be traced with unswerving regularity, but within the area to 
be described they undergo rapid change, and midway the 
tract, in the vicinity of the town of Golden, lose all recogni¬ 
tion whatsoever. For a distance of over a mile north of the 
town and an equal one to the south of it, the Dakota hog¬ 
backs have completely disappeared; the low Niobrara ridges 
cease to exist at a point about a mile north of Bear creek, 
not to again appear until the region of Van Bibber creek, 
10 miles to the north, is reached; the Laramie sandstones, 
with their coal, have gradually approached to within 500 
feet of the Archaean at Clear creek, the variation in their 
strike from that of the Triassic and Dakota outcrops below 
being apparent to the most casual observer; finally, oppo¬ 
site the center of this great topographical gap, appear the 
two great basalt-capped sedimentary masses of North and 
South Table Mountain, originally continuous, but afterwards 
cut by the waters of Clear creek, which debouches from the 
main range midway their length. 
Surface delineations .—Standing upon any of the more ele¬ 
vated points within this remarkable area, another set of 
features, second in prominence only to the ones already re¬ 
ferred to, at once strike the eye. These are the clearness with 
which the lines of stratification are delineated upon the sur¬ 
face, and the distinct tendency which they display to group 
themselves, with respect to direction, into two well marked 
assemblages: the one embracing the formations of the 
Colorado and all below, and maintaining for the greater part 
of their extent the same parallelism to the general trend of 
the foot-hills which they have held beyond the affected area; 
the other embracing the Montana and younger formations, 
and, though maintaining a parallelism of strike within them¬ 
selves, nevertheless abutting against the older formations at 
an angle In places as high even as 20°. The latter forma¬ 
tions, in fact, approach the range proper in a broad, well 
marked, and regular, inward sweeping curve, the center of 
its arch lying a short distance north of Clear creek. The 
