STRUCTURAL FEATURES IN THE FOOT-HILL REGION. 
265 
bility of the presence of an occasional fault in the place of an 
unbroken flexure as drawn in the profile is to be remarked, 
notably, in the vicinity of Gold run and north of Coon 
gulch at the points x, x of the profile. It so happens that 
here and there a space intervening between two outcrops of 
the same bed, lying in an indirect line from each other, is 
so covered that it is quite impossible to observe the position 
of the underlying strata; but since in no case a sharp break 
in the beds of the Archsean and Trias lying below the more 
affected ones has been discovered, it is preferable to sketch 
the irregularities as flexures rather than as faults. 
Concerning the recognized faults in the northern and 
southern halves of the arch, described on page 259, their true 
character now readily appears in profile IV, where, upon 
the restoration of the beds to their position in pre-Montana 
times, the fractures are, with the local exception at the south 
end of the Dakota hog-back north of Coon gulch, all found 
to be of the normal type, either vertical or hading to the 
downthrown side and away from the center of the uplift, 
and similarly developed on either flank of the elevation. 
The explanation of the normal type of fault under the at¬ 
tendant conditions may possibly be found in the readjust¬ 
ment of the strata brought about by subsidence during a 
later period. 
The profile of this ancient hill, at least on the line given 
in the figure, is one of structure rather than erosion, the 
unevenness in its outline being clearly traceable to the flex¬ 
ures underlying, the comparatively little erosion that has 
taken place over the higher portion of the arch having been 
regular in distribution, and thus having but slightly altered 
the original outline of the upheaval. The height of the 
elevation, however, has been reduced over 1,000 feet—to 
8,481—by the removal of the Niobrara, Fort Benton, and 
Dakota. 
The succession of events in the erosion, the transportation 
of the derived material, the sedimentation in the adjacent 
Montana seas, and the conditions which led up to each, are 
