162 CAKHONIKKKDUS FOKMATIONS AND KAUNAS OK COLORADO. 



exteii.si\(' ('ni)iiL;li and crilical cnoiiiih to clearly (Icinoiisli'atc the l)('\'()niaii iif^'c of tins 

 luirizon and \ iiulicate Meek's earlier judgmciil. 'i'liis fauiui occupies the major por- 

 tion of the Oui'av liinostoiie of the Sail Juan nigion and tli(^ lowci' part of the Lcad- 

 viilo limestone of central Colorado. It has been found in the Durango and Engineer 

 mountain quadrangles of the San Juan region, at Oui'ay, in the Crested Butte quad- 

 rangle, at Salida, atGlenwood Sjjrings, and on White River in north\v(\stern Colorado. 

 It seems probable that it will also be found, if sought for, in the lower part of the 

 Leadville liuK^stone at Leadville, and, in fact, wherever this formation is exposed in 

 Colorado. Perhaps the only strict exception which need be made is along the Front 

 Range, where the Millsap limestone, the probable equivalent of the Carboniferous 

 portion of the Leadville limestone, appears to lack this Devonian horizon. There 

 are areas also in which the Leadville limestone is probably missing, and there, doubt- 

 less, it may not be expected. Of the distribution of this formation, I will speak 

 a little more specifically in connection with its Mississippian fauna. 



The Ouray fauna, as I maj^ continue to call it, is not closely similar to the faunas 

 of eastern and central United States. It seems indeed to have a closer parallel in 

 the Devonian of the Ural Mountains," with which it shows some striking similarities. 

 It also has points in common Avith and seems to be related to the interior Devonian 

 of the Rocky Mountain region. The absence of this fauna in certain areas where 

 the Mississippian fauna, which it often accompanies, is present, as on the eastern 

 margin of the Front Range, and apparently over part of the Wasatch Range (e. g., 

 Rock Canyon), leads me to think that probably dej)osition was not quite continuous 

 even where both faunas occur, and both are found in limestones, and that a slight 

 unconformity may exist between the strata characterized by the Devonian and 

 Mississippian faunas in the midst of the Ouray and Leadville formations. 



CARBONIFEROUS. 

 MISSISSIPPIAN. 



The Lower Carboniferous strata of Colorado are geologically comparatively 

 unimportant by reason of their thinness, but they are widel}^ distributed and form 

 one of the richest metalliferous horizons in the entire rock series. This horizon is 

 everywhere a limestone or a dolomite, sometimes more or less interstratified with 

 shale, but owing to minor differences of lithologic character and circumstances of 

 distribution several local names have been received b}' it. In central Colorado this 

 limestone is called the Leadville limestone. In the San Juan region it is called the 

 Ouray limestone, and along the Front Range it has received the name of the Millsap 

 limestone. The lower jjortion almost everywhere contains a distinctive and unmis- 

 takable Devonian fauna. At least this fauna has been found at so many and such 



aMurchison, etc., Gtologie de la Russie, PaWontologie, London. 



