262 S. I. RMMON! OROGRAPHIC MOVEMENTS. 



■ it' Coal Measure fossils in the limestone pebbles that in s e regions form a 



characteristic feature of the conglomerates deposited immediately alter the 

 movement. < >n the other hand, the thickness of beds deposited after the 

 movement, presumably of < larboniferous age, is far greater than that of those 

 beds deposited before it: but as these are of extremely coarse material, 

 evidently deposited during the rapid abrasion of high land-masses in com* 

 paratively close proximity, il is evident thai the mere thickness of the deposil 

 is n<'t a very reliable time-gauge. 



During this movemenl some ana- were uplifted and eroded in such a way 

 that the later sediments overlapped the upturned edges of the earlier beds. 

 In others, tor instance around the shore-line of the Sawatch, the elevation 

 was of such a nature that the succeeding sediments were deposited in perfect 

 conformity, and no evidence of erosion lias been detected between the two 

 series of )>v<\<. though land plants and limited developments of coal or of 

 bituminous shahs are found at certain horizons. 



Perhaps the most remarkable feature of the sedimentation which followed 

 the movement was the great thickness of very coarse conglomerate alongthe 

 present Elk mountain ami Sangre de Cristo ranges, reaching a thickness of 

 3,000 to 6,000 feet, which are not found at all on the east front of the Col- 

 orado and Wet mountain ranges. In the Elk mountains the pebbles are 

 mostly of limestone, which are entirely wanting at corresponding horizons 

 along tin- adjoining Sawatch range. Iu the San- rede Cristo range they are 

 mostly of gneiss and granite, with some limestone pebbles; the fragments of 

 Archaean rock- in the beds opposite the Wet Mountain valley are often as 

 much as 25 or even 50 feet ill diameter, and must either have dropped from 

 adjoining steep cliffs or have been carried out into the sea by ice. To 

 account for the formation and present stratigraphical relations of the Klk 

 mountain conglomerates it is necessary to assume that during the move- 

 ment a land area was uplifted to the south of that region, from which the 

 earlier Palaeozoic beds were mostly denuded, and whose original outlines 

 <>r area can no longer l>e determined. 



The sediments that were deposited between this and the succeeding move- 

 ment near the close of the Jura were largely conglomerates, with a few mud 

 shah- and occasional thin beds of limestone. The Triassic "Red Beds" 

 near the top contain finer grained sandstones and some clays. Gypsum is 



found locally developed at various horizon-. 



In most of the beds deposited during this interval it has hitherto been im- 

 possible, in the absence of decisive palseontological evidence, to determine 

 how much <d' the entire series is represented. < mly the < iarboniferous beds 



have been found to contain molluscan remain-, and the-,- are wanting in the 



coarser grits and conglomerates. The evidence afforded by plant life has 

 thus far proved to In- somewhat meager and uncertain. In outlining geolog- 



