4 C. D. WALCOTT ALGONKIAN FORMATIONS OF MONTANA 



Feet Feet 



3a. Greenish, sandy shales, with thin layers of greenish gray, 



compact sandstone at irregular intervals 612 



&. Reddish brown, shaly sandstones 51 



c. Reddish brown, thin bedded sandstones, becoming more 



massive, compact, and almost quartzitic 50 to 75 feet 

 down. About 50 feet from the base the layers are 

 more or less cross-bedded, coarser grained, reddish 

 gray in color, and from 2 to 14 inches in thickness 970 



d. Reddish brown sandstones that, 285 feet from the top, 



gradually pass into alternating thin bedded, reddish 

 colored, sandy shales and sandstones. Toward the 

 base there is 60 feet of reddish and green, sandy 

 shales 1,362 



e. Reddish brown, thin bedded and shaly sandstones. Rip- 



ple markings and mud cracks occur abundantly in 



upper part 76 



/. Grayish red sandstone in layers 8 inches to 2 feet thick, 



alternating with shaly sandstone bands and partings . . 510 



g. Reddish brown sandstones and shaly beds 910 



4,491 



4. Alternating thin bedded, gray, hard sandstones and sandy 



shales, alternating with an occasional quartzitic sand- 

 stone ; layers 8 to 12 inches thick. At 360 feet down 

 light gray, sandy shales, slightly calcareous in places, 

 have a thickness of about 30 feet. Below, the sand- 

 stone layers are thicker, with less shaly beds, and 

 almost quartzitic in the thicker layers. At 175 feet 

 from the top a reddish brown belt 15 feet thick 

 occurs ; otherwise this great gray sandstone band and 

 a similar band below (6c) are conspicuous features in 

 the ridges, as the gray color is in strong contrast 

 with the rich, reddish brown bands. Ripple marks 

 and mud cracks are of frequent occurrence 700 700 



5. Compact, impure, gray limestone, siliceous, arenaceous, 



thin bedded, and shaly, weathering buff to yellow on 



many of its layers 198 198 



6a. Gray sandstones in layers 2 to 8 inches thick, with alter- 

 nating bands and parting of shaly sandstones 482 



b. Reddish brown, thin bedded, and shaly sandstones 68 



Sixteen feet from the top a layer about 15 inches 

 thick is nearly made up of irregularly semispherical 

 masses of Cryptozoan. The latter are calcareous in an 

 impure sandstone matrix. 



c. Gray, shaly, and thin bedded, compact sandstone 425 



975 



A bed of Cryptozoan occurs 325 feet below the sum- 

 mit, in a rough, gray sandstone layer about 4 feet 

 thick. 



