﻿io Bulletin 20 88 



Section along Boulder Creek, Philipsburg quadrangle, Montana 



Feet 



E. Dark-gray to white heavy-bedded and flaggy limestone, 



shaly toward the base (Madison limestone) 500 + 



D. Gray to black limestone in alternating beds, the latter pre- 

 dominating and distinctly magnesian, generally with sac- 

 charoidal texture (Jefferson limestone) 800 



C. Gray to brownish shale and sandstone, the latter predominate 



at the base 210 



B. Bluish gray limestone, with thin siliceous, argillaceous and 

 shale films at intervals of 1 inch to 3 inches. These inter- 

 mediate lamina? weather brownish and show in relief thin, 

 flat, pebble-like concretionary (?) sheets 275 



A. Light-gray to cream-colored, hard magnesian limestone 300 



This section differs from the two preceding sections in thq 

 absence of the Threeforks shale, which seems to be everywhere 

 wanting in the Philipsburg quadrangle. About 200 feet below 

 the base of the dark limestone series a limestone of very peculiar 

 lithologic characteristics (B of the section) is" present, which 

 carries a fauna that was referred to Mr. E. O. Ulrich and re- 

 ported by him to represent a horizon "about basal part of Upper 

 Cambrian or near top of Middle Cambrian ." Bed G of the Mel- 

 rose section is readily recognizable by the same lithologic peculi- 

 arities, although no fossils were obtained. The "pebbly lime- 

 stones" of Peale's section probably represent the same formation 

 in the Threeforks section. 



No fossils were procured from the 200 feet of beds at the base 

 of the Jefferson limestone, so that the age of the beds intervening 

 between the Cambrian and Devonian faunas remains unde- 

 termined in this region. No evidence of any stratigraphic break 

 in this part of the section was observed. 



The following fossils represent the fauna which occurs in the 

 less magnesian bands of the middle and upper half of the Jeffer- 

 son limestone in the Boulder Creek section : 



Fossils from section 2yi miles northwest of Princeton, Montana 



(16 c) 

 Favo sites cf . limit ar is 

 Productella cf . subaculeata 

 Schuchertella chemungensis var. arctostriata 



