322 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Other sections in southwestern Montana might be given which would present the same 

 general sequence with reference to the Jefferson limestone. All the sections show a limestone 

 series in which dark to nearly black limestones predominate, followed by the Madison lime- 

 stone, which is locally separated from the Jefferson by the Threeforks formation. The Jefferson 

 in all the Montana sections is preceded by limestones and shales in which the latest observed 

 faunas are of Cambrian age. 



Sections in Wyoming.— The Montana sections show a close correspondence in these char- 

 acteristic features to the southwestern Wyoming section, which follows. Tliis section occurs 

 in the westward-dipping beds of Labarge Mountain, northeast of Viola post office and west 

 of the Sayles coal mine. 



Section northeast of Viola, Wyo. 



Feet. 



J. Light to dark-gray limestone, oolitic in lower 20 feet (Madison limestone) 500± 



I. Drab shales and shaly thin-bedded magnesian and siliceous limestone 80 



H. Buff to gray limestone with much black magnesian limestone in the upper part, saccha- 

 roidal in texture, and weathering with roughly pitted surface; covered in part (Jeffer- 

 son limestone) 1, 000± 



G. Gray limestone, partly covered 700± 



F. Gray limestone, with Cambrian trilobites abundant 40 



E. Green shale and covered 300± 



D. Drab shale and covered = 30 



C. Thin-bedded gray limestone, with Cambrian trilobites abundant 10 



B. Drab shale, mostly covered 100 



A. Lead-gray limestone, checked by innumerable small joints, which are generally calcite 



filled 120 



In this section the gray and black limestone series is preceded by beds holding a Cambrian 

 fauna and followed by a limestone holding the usual Madison limestone fauna. The shale for- 

 mation (I) at the top of the magnesian limestone formation appears to occupy the position of 

 the Threeforks shale, but it is barren of fossils. Composition, texture, manner of weathering, 

 and relationship to the section all indicate that the magnesian limestone series of the section 

 is the same formation as the Jefferson limestone of the Montana sections. 



The Jefferson limestone of the Labarge Mountain section is nearly barren of fossils. The 

 only fossils obtained in it were Zaphrentis and fragments of another undetermined coral. 



Devonian roclcs in IdaTio. — The only data we have relating to the Devonian in Idaho are 

 based on a small collection of fossils made by Mr. F. B. Weeks during the summer of 1907. 

 This collection was procured from a dark limestone "in southeastern Idaho, east of Manson 

 station, Oregon Short Line Railroad." The three species represented in the collection are 

 Atrypa reticularis, Productella cf . suiaculeata, and Spirifer disjunctus cf . var. animasensis. The 

 first species is the most abundant in the fauna. The presence of Sp. disjunctus seems to indi- 

 cate an Upper Devonian horizon. The fauna is not sufficient to show whether or not the Jef- 

 ferson limestone is represented by it. Probably, however, it is from this formation. The 

 appearance of the rock, which is dark, somewhat magnesian limestone, is highly suggestive of 

 the Jefferson limestone. The evidence of the small fauna, though inconclusive, points to the 

 Jefferson limestone rather than to the Threeforks shale as its source. 



About 60 miles southeast of this locality, in northeastern Utah, the Jefferson limestone is 

 well developed. 



Sections in Utah. — Field studies in Utah were limited to the northern part of the Wasatch 

 Mountains. Numerous excellent sections of the Paleozoic are exposed by the deep canyons east 

 of Cache Valley. The canyons cut at right angles the general trend of the structure, which is 

 of the moderately folded type, few of the heavier dips exceeding 30°. Nearly vertical cliffs 

 2,000 feet or more in height alternate with slopes of every degree of inclination along the sides 

 of the canyons. * * * 



Examination of half a dozen of the canyon sections to the south of Logan Canyon has 

 shown that the Carboniferous and Devonian portions of the section may be distinguished both 

 by physical and faunal characters. In the Devonian series, generally 1,000 to 1,200 feet thick, 



