248 
ELDRIDGE. 
Page. 
Periods in the Development_ 261 
First period_ 262 
Second period_ 262 
Third period_ 263 
Fourth period__ 264 
Fifth period_ 267 
Discussion of Movements producing the present Structure_ 267 
1° Hypothesis upon which the argument rests_ 267 
2° Faults and folds—the local manifestations of forces in¬ 
volved._ 268 
3° Forces have acted with varying direction_ 268 
4° Development of the post-Niobrara fold_ 268 
5° Readjustment of forces, inducing present structure__ 270 
6° Readjustment accounted for_ 270 
7° Relation of basalt eruption to the foregoing events_ 271 
Earlier Views on the Structure of this Region_ 271 
Views of A. R. Marvine_ 271 
Views of Lester F. Ward_ 272 
Views of others_ 274 
Note.— The geological map accompanying this paper is an original plat. 
The profiles are based upon this, and are developed by construction from it 
and from one another by actual measurements, with the necessary reductions 
for thickness. The two sketches, towards the close of the text, illustrative 
of the manner in which the folding occurred and its relations to that of the 
Main Range, are, however, diagramatic, although based upon the histori¬ 
cal facts developed in the paper. 
Introduction. 
The present paper is devoted to the discussion of a type 
of geological structure recently discovered by the writer in 
the foot-hill region west of Denver, which upon detailed study 
may prove of common occurrence along the base of the Rocky 
Mountains, a recurrence of it in a less developed form having 
already been observed in the vicinity of Boulder, a few miles 
north of the area covered by the present instance. The type 
consists in a succession of non-conformities appearing one 
after another at various geological horizons, the explanation 
of which is found in the forces acting in the general uplift of 
the Colorado Range, from which have been developed cer¬ 
tain secondary forces that have from point to point brought 
about the elevations upon which the non-conformities depend. 
