88 CARBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



boiiitridiis. ami no rcferciico is made to tlieir being intcrstratified with quartzite.s. 

 The bhie liiiieMtonc aiul shakes Eiullicli prefers to regard as oldest Carboniferous 

 rather than Devonian. '•Bluisli shales that have been eroded considerably foliovf, 

 forming the bottom of a narrow valle\', and are covered in turn by a saccharoidal 

 limestone rising steeply from them." Apparentl}' following the limestone comes 

 "the red sandstone, which has not appeared for 4 or 5 miles along the line of 

 Carl)oniferou8 outcrop," nor, it might be added, has it appeared specifically men- 

 tioned before in Endlich's description, though it is probably the sandstone casually 

 referred to on page 310-311 and the same as his Arkansas sandstone. 



This section is so nearly a repetition of that made at station 53 that the correla- 

 tion of the constituent members is obvious. A conspicuous feature is the absence of 

 the basal limestone, which, however, appears to he only local, as Endlich states (page 

 310) that it reappears south of station 58 and remains entirely or partially exposed 

 southward to beyond the Arkansas. This circumstance conspires with several others 

 to render it probable that the granite in this case is not the Archean granite, but an 

 intrusive body. 



The Carboniferous formations are reported as following the Silurian to his 

 station 58, at which point the sandstones, farther north of no great dimensions, are 

 enormously developed, and the upper limestones make their appearance. Of the 

 latter a spur branches oflf to the east and runs through a granitic country for a dis- 

 tance of about 7 miles, dipping northeast to east, and then comes to an end without 

 connecting again (page 310). 



This sandstone is said to be uniform in appearance and to be greatly developed, 

 reaching a thickness of more than 5,000 feet, and even exceeding this in section h 

 south of the Ai'kansas. To this formation Endlich gives the name "Arkansas sand- 

 stone."' Running parallel with the Arkansas sandstone was found an outcrop of gray 

 and bluish limestone alreadj^ referred to, which, "for stratigraphical reasons, must 

 ]je considered as properlj^ belonging above the Arkansas sandstone." In this lime- 

 stone were found Favosites and a few other fossils. As the range of Favosites, so 

 far as known, does not extend above the lower Mississippian, the presence of this 

 genus in this limestone, if the generic identification can be relied on, seriously 

 contradicts other statements bearing evidence as to the geologic age of this bed. 

 In the Hayden atlas, moreover, this spur is represented as consisting of Lower 

 Carboniferous and Middle Carboniferous sediments. As there can be but little 

 doubt that the Lower Carboniferous of this map is Endlich's lower limestone, and 

 that his Arkansas sandstone is the Upper Carboniferous, it seems clear that the best 

 information at the time the map was constructed indicated that the limestones of the 

 spur were not a new series of limestones overlying the Arkansas sandstone, but a 

 repetition of the series lying beneath it. 



