DEVONIAN. 



321 



SectioTf, at Threeforlcs, Mont. 



Carboniferous: Madison limestone. 



Devonian: Threeforks shales. 



Feet. 



Jaspery limestones 575 



Massive limestones 350 



Laminated limestones 325 



1,250 



Upper shale 



Limestone bed shown in section. 

 Lower shales 



70 



65 



135 



Silurian (?) [Devonian of Kindle]: Jefferson limestones. . .Black limestones 640 



Cambrian: Gallatin formation. 



Pebbly limestones 145 



Dry Creek shales 30 



Mottled limestones 260 



Obolella shales 280 



Trilobite limestone 120 



835 



The Threeforks shales appear to have a much more Hmited distribution than the Jefferson 

 Hmestone. They are present, however, in the Mebose section, on Camp Creek, some 30 miles 

 west of Threeforks. The following section is seen along Camp Creek: 



Section on Camp Creek, Mont. 



Feet. 



K. 

 J. 



H. 



Gray nonmagnesian limestone (Madison limestone) 3004 



Bluish-gray argillaceous shale, huffish shale in lower part, with limestone bands near middle 



(Threeforks shale) 200± 



Black magneeian ,limestone, with minor beds of gray limestone distributed through the 



series (Jefferson limestone) 500zt 



Buff-gray hard magnesian limestone, with some shaly bands 30 



G. Buffish-gray nonmagnesian limestone, 1-inch to 3-inch laminae, separated by thin bands of 



shale 35 



F. Dark-red sandy shales 20 



E. Light-gray magnesian limestone, with some dark bands in lower half 500± 



D. Shale 100 



C. Shale and thin-bedded brownish sandstone 50 



B. Gray shale 40 



A. Quartzite weathering brownish buff 65 



The Jefferson limestone seems to reach its maximum thickness in the western part of the 

 State. In the PhUipsburg [quadrangle] nearly 1,000 feet of the Paleozoic section is represented 

 by the dark limestones of the Jefferson formation. The foUowing section indicates the rela- 

 tionship of these beds in this region, as seen along Boulder Creek, west of Princeton: 



Section along Boulder Creek, PMlipshurg quadrangle, Mont. 



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 predominating and distinctly magne- 

 sian, generally with saccharoidal texture (Jefferson limestone) 800 



Gray to brownish shale and sandstone; the latter predominates at the base 210 



Bluish-gray limestone, with thin siliceous, argillaceous, and shale films at intervals of 1 inch 

 to 3 inches. These intermediate laminae 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 the absence of the Threeforks shale, 

 which seems to be everywhere wanting in the Philipsburg quadrangle. « 



Feet. 



0. 

 B. 



a For list of fossils see the work cited. — B. W. 



48011°— 12 21 



