200 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



RfeSUMfi, BLACKSMITH FORK SECTION (continued) : 

 BLACKSMITH FORMATION: Feet 



I. Arenaceous limestone 570 



UTE FORMATION: 



1. Thin-bedded limestone 483 



2. Limestone and shales 246 



729 



S pence shale 3° 



LANGSTON FORMATION: 



1. Massive limestone 108 



2. Arenaceous limestone 390 



■ 498 



BRIGHAM FORMATION: 



I. Quartzitic sandstones (estimated) 1,232 + 



Total Middle Cambrian ^ 5,420+ 



Total section 6,647+ 



DEARBORN RIVER SECTION 



Locality. — North fork of the Dearborn River, south-southeast 

 and south ,of Mount Dearborn, Lewis and Clark Forest Reserve, 

 Montana. 



The base of the section is 4 miles above Walker's ranch at the 

 mouth of the canyon. The summit is the top of Mount Dearborn. 



CARBONIFEROUS 



Feet 



I. Brown, thin-bedded sandstone 135 



20. Massive bedded, light gray, siliceous limestone, forming a high 

 cliff and breaking into talus slopes of small angular frag- 

 ments 1,970 



Fossils : Noted Zaphrentis and Syringopora in abundance. 

 2&. Massive bedded dark gray, siliceous limestone breaking into 

 fragments ; 275 feet from the top there is a thin bed of shaly 



limestone 425 



2C. Thin-bedded, steel-gray, buff, and gray weathering limestone.. 725 

 Very few fossils were observed. A large Spirifcr and speci- 

 mens of a large Productus were noted about 400 feet from 

 the top. 



Total Carboniferous 3,255 



SILURIAN (?) 

 The strata referred to the Silurian are arenaceous limestones in 

 which no fossils were observed. It is not improbable that the upper 

 portion of them may be of Devonian age, or possibly Lower Car- 

 boniferous. 



^ See footnote on page 199. 



