RECAPITULATION OK PALEOZOIC FORMATIONS. 169 



has increased to ten times its bulk. It thus seems possible that the lower portion of 

 this series in the Pueblo quadrangle maj' represent the Fremont, though satisfactory 

 evidence upon this point is lacking, while Cross's remarks upon the restricted dis- 

 tribution of the Fremont should be borne in mind. In any event the Millsap is 

 greatly increased in thickness from its Garden Park and Can3'on outcrops. 



Endlich also recognized the Paleozoic nature of these beds, and thej' are repre- 

 sented on the Haj'den maps as an area of Lower Carboniferous, part of which is 

 included in the Pueblo quadrangle. Endlich described them as consisting of graj'- 

 ish limestones and shales, and apparently his observation relates to the Millsap lime- 

 stone alone, without including the Harding sandstone which lies beneath. 



In the San Juan region Mississippian time is repi'esented b}^ the Ouray limestone, 

 the major portion of the foi'mation, however, containing a Devonian fauna. 



The Ouray limestone is defined bj^ Cross and Spencer somewhat as follows: It 

 consists of massive beds of limestone separated b\' thin intercalations of marl or 

 shale. Certain thin bands are frequently quite coarsely crystalline, but the large 

 mass of the formation is a dense or semicrystalline limestone. The thickness is 

 about 150 feet. The greater part of this formation appears to be of Devonian age, 

 and it was only comparatively recently that a Mississippian fauna was obtained from 

 its upper portion. The latter is intimately related to the Mississippian faunas at 

 Leadville and Aspen, and also to the Waverly fauna of the Wasatch limestone of 

 Utah, the Madison limestone of Wyoming and Montana, the t3'pical Waverly of 

 Ohio, and the Chouteau limestone of Missouri. The fauna of the Millsap limestone, 

 as we know it from Perrv Park and also from Garden Park and Canyon, and that 

 of the Leadville limestone at Leadville, present a rather peculiar facies, but even 

 this fauna seems to be related to those of the early Mississippian, and it is some- 

 what singular that the Leadville fauna is more nearly allied to that of Perry and 

 Garden parks, while lithologically and stratigraphically the Leadville as a formation 

 is especially to be compared with the Leadville of Aspen and of the Crested Butte 

 region. I think we can safely regard these faunas as varying facies of a single wide- 

 spread and contempoi'aneous fauna, the differences being due in part to varying 

 environmental conditions and in part to quite a different cause. Our collections 

 from these beds are exti'emely meager, and to this circumstance can be referred 

 some of the differences at present existing. 



The Lower Carboniferous of the Haj'den sui'vej^ geologists consists in the main 

 of this bed, though it is doubtful if they were consistent throughout in recognizing 

 its limits. With them also the term was used rather as meaning the lower portion 

 of the local Carboniferous section than in its strict paleontological sense as the 

 equivalent of Mississippian. In this sense apparently the term is used in the 

 Leadville njonograph, where the Lead.ville limestone is i-eferred to the Lower 



