THE COLOEADO RANGE. 21 



off by erosion, so that the core of the fold is exposed, the proje(;tion or hori- 

 zontal section made thus by the planing off of its crest would necessarily 

 show a continuous line of outcrops along- either side of the axis of the fold, 

 in which the lowest bed of the conformable series would invariably be seen 

 at the contact of the underlying rocks which, when these beds were depos- 

 ited, formed the floor of the then existing ocean. In other words, if the 

 Rocky Mountain uplift were a typical anticlinal uplift, the sandstones of 

 the Cambrian period, which are the lowest beds of the conformable series 

 exposed, would be found continuously along the eastern flanks of the Rocky 

 Mountains wherever erosion had swept away the obscuring Tertiaries so 

 that the edges of the folded rocks could be seen. 



Since it is evident, then, that the entire series of these beds could not at 

 any time have arched over the present Archean exposures, the alternative 

 presents itself that these exposures represent an ancient continent or island 

 along whose shores they were deposited, a hypothesis which is borne out 

 by the lithological character of the beds themselves, which bear abundant 

 internal evidence, in ripple-marks, in prevailing coarseness of sediment, and 

 in the abundance of Archean pebbles in the coarser beds, that they are a 

 shore-line deposit. The varying completeness in the series of sedimentary 

 beds exposed at different points would in this case be explained by unequal 

 local erosion or elevation, by which the contact, now of a lower, now of a 

 higlier horizon, with the original Archean cliff would be laid bare. 



Inasmuch as the same evidence of shore-line conditions is found wher- 

 ever the sedimentary beds adjoining the larger masses of Archean have 

 been carefully studied, and as, moreover, in no part of the higher regions of 

 these Archean ridges have relics of sedimentary beds been found, not even 

 of the later Tertiaiy formations, as would be expected had they originally 

 arched over these ridges, it is evident that these Archean islands have never 

 been entirely submerged since they first appeared above the ocean level. 



The Colorado Range formed the most extensive of these ancient land- 

 masses, and its outlines probably did not vary essentially from those of the 

 present Archean areas. Extendingfrom Pike's Peak northward to the bound- 

 ary of the State, its dimensions were approximately one hundred and fifty 

 miles in length l)y about thirty-five to forty miles in width. To the eastward 



