386 C. W. TOMLINSON 



Richardson 1 estimates the thickness of the Three Forks forma- 

 tion in the Randolph area at 200 feet. In the Blacksmith Fork 

 section both the upper and the lower limits of the Three Forks are 

 marked by the usual sharp lithologic contrasts, yet the strata 

 between the Jefferson and the Madison total 978 feet in thickness. 

 For the most part, this sequence is composed of the usual Three 

 Forks types; but between the green shales below and the black 

 shales above there appears a 360-foot belt of blue-gray limestones 

 (Member 20B). 



Less than ten miles south of the above section, in the canyon 

 east of Paradise P.O., Utah, Kindle 2 noted no representative of the 

 Three Forks formation. In the region east of Ogden such a repre- 

 sentative is probably to be found, as suggested by Richardson, 3 

 in the reddish shales and thin-bedded limestones mentioned by 

 Blackwelder, 4 which are 250 feet thick on the South Fork of Ogden 

 River. 



In the South Fork of Big Cottonwood Canyon, about 75 miles 

 south of Blacksmith Fork, occurs the Benson limestone of Hintze, 5 

 comprising 1,032 feet of blue limestone. From a horizon in the 

 upper part of this formation Hintze collected a fauna which is very 

 like that of the Ouray limestone. His description of the Benson 

 indicates that it is lithologically very different from the typical 

 Three Forks. The belt of blue-gray limestones in the middle of 

 the Three Forks formation at Blacksmith Fork, and the upper 

 division of the Jefferson dolomite in the same section, correspond 

 roughly in character with the Benson. This fact, together with the 

 mingled Ouray-Three Forks fauna found in the Randolph quad- 

 rangle, suggests the possibility that the Ouray lithologic type 

 dovetails into the Upper Devonian rocks of the more northern and 

 western province. 



1 G. B. Richardson, op. cit., p. 412. , 



2 E. M. Kindle, "The Fauna and Stratigraphy of the Jefferson Limestone in the 

 Northern Rocky Mountain Region," Bull. Amer. Pal., IV, No. 20 (1908), 16. 



3 Op. cit., p. 412. Also Eliot Blackwelder, letter of April 29. 1915. 



4 Eliot Blackwelder, "New light on the Geology of the Wasatch Mountains, 

 Utah," Bull. Geol. Soc. Amer., XXI (1910), 528-29. 



5 F. F. Hintze, Jr., op. cit., pp. 88-142. 



