Douglass : Geology of Southwestern Montana. 425 



that it will prove to be earliest Pennsylvanian, and be equivalent to 

 beds which in the Central and Eastern States have been variously 

 called, now Millstone Grit, now Coal Measure conglomerate, and 

 again the Pottsville group. As this fauna is as yet imperfectly known, 

 my opinion is merely tentative, and the fauna from Montana may be, 

 as I at first believed, a modification of one of the Mississippian faunas- 

 " (8) is Rocky Mountain Jurassic. 



" (9) and (10) are evidently the same and belong to the Devonian 

 and, I have little doubt, to the Upper Devonian." 



Zeigler's Canon, Bighole River. — This is southwest of Twin 

 Bridges, above Zeigler's Springs. A detailed section is given on 

 plate XV. The lowest rock exposed here is a heavy quartzyte suc- 

 ceeded by stratified quartzytes which in places contain fossils. The 

 following list of species was supplied by Mr. Raymond. 



" Lower Canon of Bighole River, above Zeigler's Springs, Montana. 

 Lingula sp. ind. 

 Camarotcechia sp. ind. 

 C. metallica White. 

 Pugnax Utah Marcou. 

 Productus sp. ind. 

 Cleiothyris orbiciihifis McChesney. 

 AviculopecteJi cf. A. lueherensis Hall and ^^'hitfield. 

 Aviculopecten cf. A. ut alien sis Meek. 

 "An Upper Carboniferous faunule." 



PERMIAN? 



In the Zeigler's Canon section, the Upper Carboniferous quartzytes 

 are overlaid by shales, apparently carbonaceous, with layers of lime- 

 stone, and then by 150 feet or more of thin bedded limestones with 

 layers of shales. The limestone weathers to a uniform chocolate 

 brown on the surface. Interbedded with these are dark slates. These 

 limestones and slates are very fossiliferous but the fossils are mostly of 

 one species, a Z///i;//Az. These beds occur also in the Frying-Pan 

 Basin west of Dillon. I have not seen them in any other places. 



Some of these fossils with other sets were sent to T. W. Stanton of 

 the United States Geological Survey. The following is his report on 

 them. 



"Lower Bighole Cafion, below Zeigler's Springs, Montana. 

 Lim^ula. 



