20 SURVEY or COLORADO AND NEW MEXICO. 



the Jurassic beds capped with the sandstones of No. 1, inclining 8° 

 Then comes a series of red beds dipping 1° to 3°. The inner ridge, or 

 "hog-back,'- is the largest of all — one hundred and fifty to two hundred 

 feet high — is partlj^ covered on the east, or sloping side, with the loose 

 red sand of the triassic; and on the west or abrupt side, is revealed a 

 considerable thickness of limestone, which I suppose to be of carbonif- 

 erous age. This ridge is remarkably furrowed on the eastern slope by 

 streams, but is too high up on th« mountain side to be divided by the 

 currents into the peculiar conical fragments, as the lower ridges are. 

 And heuce it presents an almost unbroken flank for miles. There is 

 no better exhibition of the sedimentary rocks, with all their i^eculiar 

 characteristics and irregularities, than from the head of Box Elder Creek 

 to Caclie a la Poudre, where the belt of upheaved sedimentary rocks 

 varies from five to fifteen miles in width. No one could stand on the 

 summit of one of these ridges and turn his eye westward over the 

 series, rising like steps to the mountain summit, and then looking 

 eastward across the broad level plain where the smaller ridges die out 

 in the prairies, like waves of the sea, without arriving at once to a clear 

 conception of the plan of the elevation of the Eocky Mountain range. 



The main range of the mountains is really a giaantic anticlinal, and 

 all the lower ranges and ridges are only monoclinals, descending, step- 

 like, to the plains on each side of the central axis. There are some vari- 

 ations from this rule at many localities, which 1 shall attemx)t to explain 

 from time to time in the pi-oper i)lace. 



One of these ridges is quite conspicuous to the eye, from the fact 

 that it is capped with a heavy bed of sandstone' which I have always re- 

 garded as transition or No. 1 (?) because it holds a i)osition between 

 the well-defined cretaceous beds Nos. 2 and 3, and the j urassic. 



Not a single well-marked tossil, animal or vegetable, has ever been 

 found in this group of strata along the flanks of the mountains 5 yet I 

 do not hesitate to regard them as lower cretaceous. 



On the summits of all these ridges are numerous piles of rocks which 

 have been erected by Indians in years past as monuments or land-marks. 



Inside of the sedimentary ridges are the metamorphic rocks, mostly 

 red feldspathic granites, disintegrating readily, and easily detected by 

 the eye at a distance by their style of weathering. Still further west- 

 ward are the lofty snow-capped ranges, whose eternal snows form the 

 sources of the permanent streams of the country. 



It seems clear to me that the more recent sedimentary formations, up 

 to the lignite tertiary, inclusive, once extended over the whole country. 

 Perhaps no finer locality exists in the West for the careful study of the 

 different sedimentary formations and their relations to the nietamori:)hic 

 rocks than along the overland stage road from Laramie to Denver. 



Before reaching Laporte the road passes for twenty miles or more 

 through ridge after ridge remarkably well exposed. After emerging 

 from the mountains eastward it runs south for four or five miles along 

 the cretaceous beds with their upturned edges on the east side, and the 

 Jurassic and triassic (?) on the west forming a slope much like the roof 

 of a house. The valley between the two ridges through which the road 

 runs is a beautiful one. 



South of Big Thompson Creek the belt of upheaved ridges, or un- 

 changed rocks, becomes quite narrow, and continues so to Denver, and 

 even beyond. 



The cretaceous rocks in this region, though plain to one who has 

 carefully studied them on the TJpi)er Missouri, are not seijarated into 

 well-marked divisions. If they had first been studied along the foot of the 



