418 N. H. DARTON — STRATIGRAPHY OF THE BLACK HILLS. ETC. 



horizon. The underlying series of Red beds contain the southern exten- 

 sion of the upper Carboniferous (Pennsylvanian) limestones which were 

 traced southward to beyond Belleview, where they gradually thin out. 

 In another section measured a short distance northwest of La Porte 

 similar features were found. The supposed representative of the Ten- 

 sleep sandstone is prominent. It is overlain by about 150 feet of soft, red 

 shale, at the' top of which there is a series of limestones 30 feet thick- 

 the latter almost precisely similar in aspect and relations to the Minne- 

 kahta limestone in the Black hills and at the north end of the Laramie 

 mountains. Next above there are several hundred feet of typical red 

 sandy shales of the upper Chugwater, surmounted by 60 feet of the 

 pinkish red, massive sandstone constituting the top of the formation- 

 In their extension southward the lower Red beds vary greatly in thick- 

 ness, for they lie on an irregular surface of granite and higher beds over- 

 lap lower ones at various horizons. On Little Thompson creek the 

 entire Red bed series has a thickness of about 1,100 feet, of which the 

 upper 350 are regarded as Chugwater (upper Wyoming), having near 

 its base a thin bed of limestone as in the section northward. 



There are extensive exposures of the Red beds at Lyons clearly illus- 

 trating the stratigraphy. At the base, lying on the granite, are several 

 hundred feet of coarse arkosic red sandstones with some gray mottlings 

 and gray layers. These are capped b}' 80 feet or more of fine, even 

 grained, pale reddish sandstone, in part thin bedded, which is exten- 

 sively quarried. It is believed to represent the Tensleep sandstone of 

 the Bighorn region, and is overlain by the usual soft, red, sandy shales 

 typical of the Chugwater formation (upper Wyoming) in the following 

 succession : 



Section of Chugwater Formation at Lyons, Colorado 



Feet 



Red and green "joint clays " (Morrison) 



Talus 25 



Buff and yellowish buff sandstone 30 



Dirty red sandstone 30 



Red sandy shales 200zh 



Limestone, thin bedded 15 



Red shales or sandstone 80 



The thin bedded limestone is very similar to the Minnekahta lime- 

 stone of the Black hills and central eastern Wyoming. It yielded a few 

 poorly preserved fossils, which unfortunately afforded no decisive evi- 

 dence as to the age of the beds. They comprised a small gasteropod, 

 supposed to be Natica or Naticopsis, and some small, indeterminate 

 pelecypods, which may be either Triassic or Carboniferous. 



