RECAPITULATION OF PALEOZOIC FORMATIONS. 



It is proposed in the following- pages to give a brief summary of the historical 

 geology of the Paleozoic strata of Colorado. My discussion will lie limited geolog- 

 ically to data furnished by the literature, and paleontologically to the literature and 

 to the Carljoniferous faunas which have come into my hands. Perhaps a considera- 

 tion of the Carboniferous strata is all that is strictly appropriate, but the distribu- 

 tion of the older Paleozoics is not without a bearing upon the mutual relations of 

 land and water during Carboniferous time, and this in turn is prime in importance in 

 the matter of the relations of the Carboniferous sediments and faunas. 



The presence of Paleozoic sediments is demonstrated over extensive areas in 

 Colorado. They are concealed over large areas b}- later deposits, and in places their 

 absence is an established fact; but I believe that originality thej' may have existed 

 almost continuously over the State. Even if preserved from post-Paleozoic erosion, 

 however, it seems improbable that the different groups would have had the same 

 distribution, owing to erosion and disturbances within Paleozoic time itself. 



The only Paleozoic strata at present known in Colorado are those of the Cam- 

 brian, Ordovician, Devonian, Mississippian, and Pennsylvanian eras, which are rep- 

 resented in an imperfect and fragmentary manner. This condition is doubtless in 

 part due to original deposition, but is, I believe, in larger measure than generally 

 admitted, the effect of periods of Paleozoic erosion. The Cambrian, Ordovician, 

 Devonian, and Mississippian beds are reduced to comparatively insignificant thick- 

 ness, and though these strata underlie broad areas, their outcrop is chiefly linear, 

 following that of the present Archean and Algonkian masses. In some cases Carbon- 

 iferous or later deposits are brought by overlap into direct contact with the Archean. 



Some of the areas where earh' Paleozoic sediments might be expected, but are 

 apparently lacking, are very extensive. Much of the work done in Colorado so far 

 has been of a reconnaissance character, greatly deficient in detailed measured sec- 

 tions, careful tracing of beds, and the accumulation of paleontologic evidence. Thus 

 it seems probable that thin measures of Cambrian or other Paleozoic sediments may 

 have been overlooked, but in some cases thej'^ are obviously lacking. 



It is generally true that where one of these earlier Paleozoic groups is found the 

 others also are present, but while this holds good in a general way, important excep- 

 tions occur. 



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