EECAPITULATION OF PALEOZOIC FORMATIONS. 179 



is that to which most frequent reference has been made. It has seldom been described 

 in detail save in the sections mentioned above, and to cite and comment upon all the 

 references would be fatiguing and unprofitable. It is, however, seldom possible to 

 recognize in these reconnaissance reports either the Weber formation as a distinct 

 unit or the two divisions of the original Maroon, for one of which the name Weber 

 grits was subsequently used. From facts brought out by the literature, some of 

 which have been repeated here, it seems safe to infer that the Maroon formation, 

 though differing somewhat in character from point to point, is persistent over the 

 Elk Mountain, Grand River, and South Park regions, being present wherever the 

 horizon for it is brought to view. The Weber formation, however, much thinner 

 than the Maroon and less prominent than the Leadville formation, can hardly be 

 recognized outside of a few detailed sections. In Fossil Ridge 45 feet of light shale, 

 followed b}^ 150 feet of light blue and 37ellow limestone and quartzite and 50 feet of 

 yellow, reddish, and whitish shales, maj^ belong to this formation. They rest upon 

 the Leadville. The occurrence of the Weber at Crested Butte, at Aspen, on Eagle 

 River, at Red Cliff, and in the Tenmile and Leadville districts has already been 

 described. South of Leadville I have not been able to identify it in the South Park 

 region, though this is perhaps due to a lack of detailed information. If present, this 

 series would probably contain the gypsum beds mentioned by Stevenson. In two 

 sections described by Endlich it may be represented by part of the series which 

 have been taken to belong to the Leadville limestone. This consists in the one case 

 of gray and brown shale and dark-blue limestone, and in the other of bluish shale 

 and gray saccharoidal limestone. 



The great mass of the Upper Carboniferous sandstones and conglomerates 

 appears to have been at one time continuous over most of cential Colorado, and its 

 distribution is still very wide. These strata seem to be generally present over the 

 Grand River region, the Elk Mountains, and the South Park region, and they form 

 the mass of the Sangre de Cristo Range southward to Costillo Peak, near the 

 southern border of the State. Sevei'al geologists have described their occurrence in 

 this range, but records of detailed study are rare. Endlich gave to them the name 

 of the Arkansas sandstone, though but little satisfaction can be obtained from his 

 reports. At one point in the San Luis district he describes the Arkansas sandstone 

 as over a mile in thickness, consisting of heavy beds of red sandstone more or less 

 interstratified with dark-brown shale and containing isolated beds of limestone. In his 

 Southeastern district it appears to be made up chiefly of red sandstone intersti'atified 

 with red shale and blue limestone. Stevenson says but little of these strata as they 

 appear in the northern part of the range, but describes in more detail their occur- 

 rence m the southern part, where he recognizes two series, both of which are 

 included in the Carboniferous. The lower one has a total thickness of 3,727 



