258 
ELDRIDGE. 
tion, and its basal sandstones form along their trend a char¬ 
acteristic series of combs. 
Arapahoe and Denver .—The formations above the Laramie, 
although in reality markedly unconformable with it and 
with each other throughout the broad area over which they 
have been deposited, nevertheless in the present tract so 
closely follow the former in strike and dip that they display 
no peculiarities worthy of note in the present discussion, 
and in fact are only incidentally connected with the special 
geological history here discussed. 
Special irregularities .—The two irregularities in the super¬ 
ficial relations of the strata noticed upon the map—the one 
just south of Ralston creek in the vicinity of the eruptive 
dike, where a block of strata has been displaced to the east¬ 
ward, the other immediately north of Coal creek, where the 
Dakota and formations below have been thrown into the 
greatest relative confusion—are not connected in any way 
with the phenomena which form the subject of this paper, 
and will therefore only be alluded to as occasion demands. 
Structural Features. 
Dips .—A geological cross-section along Bear creek would 
present a gradual increase in the dip of the several forma¬ 
tions from the Archaean outward at a rate about as follows: 
35° E. for the Trias; 38°-40° for the Dakota, Fort Benton, 
and Niobrara; 45° for the lower part of the Fort Pierre, in¬ 
creasing to 55°-65° in the upper part; 65°-80° from base to 
summit for the Fox Hills, and 80°-90° and overthrown for 
the Laramie, Arapahoe, and lower members of the Denver 
formation. Three or four miles north of Bear creek, 10°- 
15° may be added to the lesser of the foregoing dips, while 
from Coon gulch to the vicinity of the hog-back first north 
of Golden the formations of higher dip, having now become 
vertical or slightly overthrown, remain so, and the Triassic 
beds alone have an inclination under 80° or 90°. North of 
this, where regularity in the formations once more prevails, 
