STRUCT UK AL FEATURES IN THE FOOT-HILL REGION. 267 
arenaceous beds of the Fox Hills—are, however, not confined 
to the area under consideration, and therefore bear no rela¬ 
tion to the phenomena here discussed. 
With the general movement at the close of the Laramie 
and those which produced the non-conformities between the 
Arapahoe and Denver formations the peculiar structural 
features here described have nothing to do. 
Fifth period. —Upon comparing profile IV with the present 
surface section of the same beds upon the general map of 
the region, the early relations between the arched and hori¬ 
zontal strata, as shown in the profile, are observed in later 
times to have completely interchanged. The once highly 
arched strata below the line of non-conformity have now 
assumed a practically direct trend, w r hile the strata above 
the line of non-conformity, originally horizontal, have at 
the present time a well-defined inward sweep towards the 
mountains, reaching their limit of deviation in the vicinity 
of Golden, or, looking at the latter feature with reference 
to the profile itself, the Laramie and overlying strata have 
acquired a downward bend at the center of the area, directly 
over the crown of the arch of post-Niobrara times. Com¬ 
pare also figures 1 and 2, following. 
The final movement which produced the present structural 
conditions, together with the outpouring of the lavas of Table 
Mountain midway the period of the Denver formation, are 
regarded as constituting the fifth and closing stage in the 
geological development of the area under discussion. 
Discussion of Movements producing the present Structure. 
ls£. Statement of the hypothesis upon which the argument 
rests. —It is believed from the not infrequent occurrence, 
either within the present area or in other parts of the Eocky 
Mountains, of compound folds of the S type and of otherwise 
contorted strata, from the presence of reversed faults, and 
from the occurrence of the well-known folds 6 en echelon ” 
that the theory of lateral compression as the means by which 
