214 OARBONIFEKOUS FOKMATIONS AND FAUNAS OK COLORADO. 



the clcxiilcd surracr lius liccii reduced by proliiieled erosion to ;i liase-level, erosional 

 uiu-oiiroriiii(y ill local exposures is liiru'oly oliscurod. 



1 shall \-eiiture to say but little ii))out Paleozoic time earlier than the Cai-- 

 honit'eruus. It seems to me, however, that the evidenee, briefly and partially sub- 

 nutted, indicates that conditions were not uniform in successive epochs, and that 

 sedimentation was not continuous during Paleozoic time; that it was not only 

 interrupted, but one migiit almost say was reversed. Indeed, the evidence coming 

 before me seems to indicate uniform contemporaneous conditions, sediments, and 

 faunas over remai'kablv extensive areas in the West, with changes to other contempo- 

 raneous conditions equally widespread. It is possible that some of the present 

 Ai'chean areas were islands during Cambrian time, yet too much weight should 

 not attach itself to the siliceous character and basal conglomerate, for the wide 

 distribution of moderately coarse conglomeratic material not linearly along a coast 

 but apparently in an areal sheet is a common geologic occurrence. On the other 

 hand, the different calcareous beds I conceive, accepting the common interpreta- 

 tion, to repreisent moderately deep clear waters. I can not believe in the forma- 

 tion of reasonablj' pure calcareous sediments close to an Archean land mass save 

 as an exceptional occurrence. The overlap of a limestone series upon the Archean 

 or Algonkian, as noted in the case of the Ouraj' limestone of the San Juan region, is 

 significant in indicating important hypsometric changes. 



I would conclude, from the foregoing considerations, not that there were no 

 land masses during Paleozoic time, but that they were independent, and not neces- 

 sarilj' continuous from period to period; and that the consideration of geographic 

 conditions should be epochal, while to speak of them in connection with Paleozoic 

 time as a whole is fallacious. But the accumulation of many more facts, both in 

 stratigraphy and in paleontology, is necessary to complete the evidence. While per- 

 haps an opinion has been expressed regarding early Paleozoic conditions stronger and 

 in more general terms than the facts really warrant, it is my belief that during, Lead- 

 ville time at least the questionable Archean islands were submerged beneath a wide- 

 spread Mississippian sea. This opinion rests chiefly upon the persistent lithologic 

 and paleontologic characters displayed by the rocks of this period. The Waverly 

 horizon occurs in a large number of our Western States. It is nearly everywhere 

 a limestone formation, and everywhere characterized by essentiallj^ the same fauna. 

 This is quite true of the Waverly horizon of Colorado — the Leadville limestone. It 

 seems likely that the proximity to land, if such existed, would be indicated by a 

 change in the sedimentation if not in the fauna. Nowhere does this seem to be the 

 case in Colorado. The small isolated area of Paleozoic outcrop in Manitou Park and 

 the long strip in the Mosquito Range are frequently accounted for as having been 

 bays and inlets, but the character of the fauna seems to be essentially the same as 



