122 C.W. TOMLINSON 



such variations are conspicuous or important they are specifically 

 described for the locality where they were noted. 



The standard list of members, together with the detailed correla- 

 tion tables (Figs. 2, 3), in effect furnishes a compound section for 

 17 different localities in the central Rocky Mountain region. 



Method of correlation. — In making the correlations -here set forth 

 the notes and the specimens from each section were carefully com- 

 pared with the notes and the specimens from every other section, 

 at first singly, then in groups. When a thorough and comprehen- 

 sive tentative plan of correlation had been completed, all of the 

 specimens from all the sections were laid out on a specially prepared 

 floor, marked off into intersecting columns and rows, so that com- 

 parison of all the specimens thought to belong to a given horizon 

 could be made at once, and at the same time all possible alterations 

 in the proposed plan of correlation could be considered with the 

 specimens in view. Happily, the original plan stood the test with 

 very few changes, and those were of minor consequence. 



All available paleontological data were carefully studied to 

 determine as accurately as possible the age of the several members. 



This correlation is not to be considered as final in all details, and 

 even a few of its larger features are still clouded by uncertainty 

 due to lack of data. The points in doubt are indicated in the dia- 

 grams and discussed in the pages following. 



Sources of data. — The 7 sections, other than those measured by 

 the writer, which are embodied in the correlation were taken from 

 the following sources: 



Eureka District, Nevada.— Arnold Hague, "Geology of the Eureka District, 

 Nevada," U.S. Geol. Survey, Monographs, XX (1892). 



Randolph quadrangle, Utah.—G. B. Richardson, "The Paleozoic Section 

 in Northern Utah," Amer. Jour. Sci., 4th Ser., XXXVI (1913), 406-18. 



Labarge Mountain, Wyoming.— Eliot Blackwelder, unpublished manu- 

 scripts, U.S. Geol. Survey; E. M. Kindle, "The Fauna and Stratigraphy of the 

 Jefferson Limestone in the Northern Rocky Mountain Region," Bull. Amer. 

 Pal., IV, No. 20 (1908), 12-13. 



Survey Peak, Wyoming.— J. P. Iddings and W. H. Weed, "Descriptive 

 Geology of the Northern End of the Teton Range," U.S. Geol. Survey, Mono- 



hs, XXXII, Part 2 (1899), chap, iv, p. 180. 



Princeton, Montana.— E. M. Kindle, op. cit., p. 10. 



Melrose, Montana.— E. M. Kindle, op. cit., p. 9. 



