96 GEOLOGY OF THE DENVER BASIK 



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, 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 in a degree speculative; but the 

 inferences are, first, that soon after the completion of the Niobrara period 

 elevation began, and so much of the hill as is above the altitude indicated 

 in the section (Profile IV, PI. X) by the line marking the upper layers of 

 the Niobrara was then, sooner or later, brought within the erosive power 

 of waves or currents, and the sediments last laid down, being now brought 

 into a favorable position, and still in a condition sufficiently soft to permit 

 their being easily broken down and comminuted, were removed by the 

 transporting powers of the waters washing them; secondly, that the condi- 

 tions of sedimentation in the immediate seas were the same as those in all 

 mediterranean or large inland seas or along the margins of the continents 

 at the present day — that is, there was comparatively dee}) and quiet water 

 at a distance somewhat remote from the nearest coast line, which permitted 

 the tpiiet settling of the sediments forming the clays of the Montana group, 

 and corresponded to those under which the blue mud of subcontinental 

 areas is now being deposited. 



The apparently complete removal over the space originally covered 

 by them of the materials resulting from the breaking down of the early 

 Cretaceous strata is somewhat striking, but it may readily lie accounted 

 for in the nature of the formations removed and in the action of waves and 

 currents throughout the longtime the higher parts of the elevation were 

 probably subjected to them. Furthermore, it can not be positively asserted 

 that the line of unconformity is as (dear of debris as represented, since on 

 the steeper flanks of the arch it is rare that the beds above this line can be 

 traced to actual contact with those below; still further, it is to be remem- 

 bered that nothing whatever is known of the conditions on other profiles of 

 this ancient hill. During the deposition of the beds of the Montana group 

 gradual subsidence of the area at a generally uniform rate must have taken 

 place, the sedimentation, with two exceptions, being that of quiet and deep 



