22 Annals of the Carnegie Museum. 



cognized here there is a general persistence of a lower and upper shaly 

 member separated by a more massive limestone. There are, however, 

 no true argillaceous shales in the formation, as exposed in the southern 

 part of the quadrangle. 



Some of the sections of the Three Forks Formation measured by Dr. 

 Weed* in the northwest corner of the Yellowstone Park are similar in 

 lithologic character to the section already given. Three of these 

 sections are as follows: 



Crowfoot Ridge Section. 



Buff and red fissile argillaceous and siliceous limestone. . . 30 feet. 

 Crystalline magnesian limestone, generally dense and mas- 

 sive 50 



Limestone, impure and argillaceous, in alternating thin 



fissile, and massive gray beds 100 



Total 180 feet. 



Antler Peak Section. 



Light gray limestone, somewhat massive 40 feet. 



Dark brownish gray arenaceous limestone 130 



Total 170 feet. 



Bighorn Pass Section. 



Gray crystalline limestone 80 db feet. 



Dark bluish gray massive argillaceous limestone 20 



Alternating beds of massive gray arenaceous limestone and 



fissile light gray limestone 40 



Total 140 ± feet. 



East of the Yellowstone Park in the region described in the Absaroka 

 folio of Central Wyoming, Dr. Weed* has identified the Three Forks 

 Formation, which there has an average thickness of about 250 feet. 

 He describes the formation as consisting of bluish gray limestone at 

 the base, alternating with shaly beds and fine clays. These pass 

 upward into bedded limestones generally bright purple and blue, with 

 intercalated thin layers of indurated earthy and sandy material. 

 Recurring alternations abound, but limestone is the prevailing rock. 

 In places near the top of the formation the shaly beds exhibit bright 

 red and orange tints. Localities yielding small groupings of a marine 

 Devonian fauna occur at several places in the Absaroka district. 



The Three Forks Formation has been recognized by Dr. Kindle* in 



*Weed, W. II., Mono., 32, pt. 2, pp. 7, 22, and 26, 1899. 

 » Weed, W. H., Atlas Folio. U. S. G. S., No. 52, 1899. 

 • Kindle, E. M., Bull. Am. Pal., No. 20, p. 12, 1908. 



