374 C. W. TOM LIN SON 



These descriptions show a marked resemblance to the section 

 at Blacksmith Fork, from the lower part of the Jefferson down into 

 the Laketown dolomite. 



On the south slope of Quartz Peak in the Pahranagat Range in 

 southern Nevada, about 140 miles south of Eureka, the Lone 

 Mountain includes the following member: 



2. 335 feet. Massive bedded dark siliceous limestone, with a stratum (not 

 far above the base) 30 feet thick, almost made up of a species of Pentamerus. 1 



This, again, is strikingly like the Laketown. 



Is the Laketown dolomite in part Devonian? — The uppermost 

 member of the Laketown dolomite in the Blacksmith Fork section, 

 202 feet thick, is of much the same type as the Leigh formation 

 of northwestern Wyoming. It immediately underlies beds of 

 typical Jefferson dolomite. In the Teton River section the basal 

 member (23 feet thick) of Blackwelder's 2 Darby (Jefferson) forma- 

 tion is of similar character, and is separated by an erosion surface 

 from the underlying Leigh formation. In the Livingston Peak 

 section there is a member, 21 feet in thickness, which is identical 

 in type with the true Leigh, but which lies above the cliff -making 

 Upper Bighorn dolomite, at the base of the Jefferson dolomite. 

 In the Crandall Creek section the corresponding member, 26 feet 

 thick, overlies a 47-foot sequence of variegated beds which lie 

 disconformably upon the Upper Bighorn. At Livingston Peak and 

 at Teton River, ostracods like those which are characteristic of the 

 Leigh formation were found in this repetition of the Leigh type 

 at the base of the Devonian system. 



In brief, the uppermost member of the Laketown dolomite in 

 northern Utah corresponds in lithologic character, and in relation 

 to the overlying Jefferson dolomite, to the member which farther 

 north appears to have been the introductory deposit of the first 

 Devonian submergence. This relation suggests that the Utah 

 member in question belongs with the Devonian rather than with 

 the Silurian system. This interpretation has been followed in the 

 correlation tables and diagrams accompanying this thesis, where the 

 beds just discussed appear as Member 2 of the Devonian system. 



1 Arnold Hague, op. cil., p. 196. 



2 Eliot Blackwelder, unpublished manuscript, U.S. Geol. Survey. 



