256 C. W. TOMLINSON 



tion of beds both above and below) with the base of the known 

 Richmond part of the Bighorn in the type locality, it probably 

 represents the hiatus which was inferred by Darton between the 

 Trenton and Richmond members of the Bighorn. 



In the Teton Range, there is likewise an unconformity at the 

 base of Member 6. Blackwelder 1 proposes the recognition of 

 Members 6 and 7 in that region, and of corresponding strata in the 

 Gros Ventre Range, as a distinct formation, to be called the Leigh, 

 from its typical development on Leigh Creek, in the Teton Range. 

 In view of the fact that this group of strata, in its type locality, 

 is bounded both above and below by unconformity, and is lithologi- 

 cally quite distinct from the underlying massive member (Member 



5 is not present in the Teton River section), its recognition as a 

 separate formation seems justified. In the Absaroka Range the 

 corresponding beds differ little in character from the upper part of 

 the Trenton series (Member 5), but are marked off from it by uncon- 

 formity, as just described. 



Between Members 4 and 8 of the Livingston Peak section, light- 

 colored dolomites of the Leigh type occur interbedded with darker, 

 gray-brown, more coarsely crystalline dolomites. In the Black- 

 smith Fork section there is an interbedding of light and dark 

 strata through a thickness of 130 feet above the conglomeratic 

 horizon, which is taken as the probable base of the Richmond series. 

 Above this sequence there is an 8-foot stratum corresponding 

 closely to the typical Leigh in character, and directly underlying 

 the main massive part of the Fish Haven, which is correlated with 

 Member 8. The first sediments deposited after the pre-Richmond 

 emergence seem to be more variable in character from place to 

 place than are the strata above them, or the members of the Trenton 

 series. 



Members 8 and p. — Member 8 is in some places, in lithologic 

 characters, essentially similar to Member 4, but is in no case quite 

 so thick as the latter. On Goose Creek Ridge there are only two 

 12-foot massive beds of this type, themselves separated by 20 feet 

 of less resistant dolomites, between the typical Leigh (Members 



6 and 7) below and the main fossiliferous, thin-bedded part of the 



1 Eliot Blackwelder, personal note. 



