142 ■ CARUONIKEROUS FORMATIONS AND FAUNAS OF COLORADO. 



arc, I I'ciir, not to !»' wholly ri^liccl on. In one case he dcscribi^s at a certain "station 

 56" yellow and brown (|uartzitos resting upon porphyritic granite and followed by 

 white and pink ([nartzitc. then l)y shales and yellow ((uartzite, and tinall}^ by blue 

 limestone and gray shales, which are probably Carboniferous. The other section, 

 made at station 53, shows a dift'erent series. Kesting on granite is a heavy quartzitic 

 limestone, which can hardly l)e older than the Ordovieian, and this is followed by 

 thin shales, gray limestone, white, yellow, and pink quartzite and red sandstone, 

 yellow and brown sandy shale, graj' limestone, gray shale, sandy shale, dai'k blue 

 limestone, and brown sandstone. The gva.y limestone near the top of the section 

 appears to belong to the Lower Carboniferous. 



The section first mentioned can probablj' be best interpreted by taking the 

 pprphyritic granite as an intrusive, and considering the basal quartzite as the Parting 

 formation and equivalent to the very similar quartzite of the other section made at 

 station 53. Unless the granite of the latter is also an intrusive it would appear that 

 through noudeposition or ancient erosion the Sawatch is wanting in places even in 

 the South Park region, so that the Yule rests directly upon the Archean. 



Endlich found the "Silm-ian," under which title the Sawatch quartzite is else- 

 where included, in small quantities south of the Arkansas, and the Hayden Atlas 

 shows the Silurian color in the northern end of the Sangre de Cristo region bordering 

 the river. In section c of the San Luis district Endlich describes the Silurian as 

 consisting of light-colored quartzites of j^ellowish, bluish, and reddish tints, con- 

 formabh' stratified with the superincumbent gra}' to bluish limestone with siliceous 

 segregations (p. 338). These beds certainlj^ suggest the Sawatch quartzite and 

 Yule limestone of standard sections, and Endlich states that lithologicallj' thej^ are 

 identical with the Silurian north of the Arkansas. As described by Endlich, the 

 lithologic resemblance is in some cases striking, but an unexplained contradiction 

 seems to exist in stratigraphic position. In Endlich's Fossil Ridge section (Elk 

 Mountain region) only the limestone is cited, the quartzite, if present, probably 

 lying unexposed beneath it. In the series described as occurring at station 53, north 

 of the Arkansas, both quartzite and limestone are found, but with their relative 

 position the reverse of that recorded in section c, for the quartzite there rests upon, 

 not under, the limestone. In the section at station 56, also north of the Arkansas, 

 only the quartzite is found, resting upon a porph3'ritic rock which probablj' can 

 be best interpreted as an intrusive concealing the limestone which, as at station 53, 

 near by, lies beneath the quartzite. From its reported position in the two sections 

 north of the Arkansas, the quartzite must be regarded as the Parting formation, 

 while in that cited from section c it must be the Sa,watch. It seems, therefore, 

 either that Endlich's correlation of the beds is faulty, or, what is not improbable, 

 that his observations as to the position of the quartzite is in error in one case or the 

 other. 



