

210 THE CAMBRIAN. Iiiull.81. 



in which 67 feet of sandstone ocmr resting upon the granite. Of these 



sections Dr. Peale says : 



A comparison of the sections given above shows that the Potsdam group is repre- 

 sented by sandstones having a thickness of from 60 to 80 feet, while the beds that 

 represent the Quebec group are a little over 100 feet thick. 1 



References to the sandstone supposed to be Potsdam are also found 

 on pages 226, 236, 242, and 255. 



During the field season of 1874 Dr. A. C. Peale found on Eagle River 

 a series of beds resting on the gneiss and schist. From their position 

 and lithologic relations to corresponding beds seen in the Colorado 

 Range in 1873 the lower layers are referred to the Potsdam group. It 

 is represented by a bed of white quartzite. 2 



A reference to the probable occurrence of the Potsdam horizon upon 

 the eastern side of the Colorado Range is made by Mr. Arnold Hague, j 

 in his general description of the geology of the range. From the fact 

 that a sandstone occurs in the Black Hills, and contains fossils of ai 

 Primordial type, he thinks the sandstone occupying a similar strati- 

 graphic position in the Colorado Range will be found to contain the 

 same fauna. 3 



On the geological map of Colorado, published by Dr. Hayden in 1877, 

 the quartzite and the limestone referred to the Potsdam series are in- 

 cluded with the Silurian, and their geographic distribution is merged _ 

 with the latter on the map. 



In his synopsis of the geological formations found in Colorado Dr. F. 

 M. Endlich tabulates the localities and formation of the "Potsdam 

 group." 4 



When describing the Paleozoic rocks of the Mosquito Range in cen 

 tral Colorado, Mr. S. F. Emmons states that the Cambrian is represente 

 by quartzites passing gradually upward into calcareous shales, wit 

 limestones of probably Silurian age above, the aggregate thickness o 

 the two being about 400 feet. 5 In the tabulation of the Mosquito se 

 tion the Cambrian white quartzite is given a thickness of from 150 t 

 200 feet before passing into calcareous and argillaceous shales above. 8 

 The only fossil remains found in this series occur in a bed of greenish 

 chloritic slates on the east flank of Quandary Peak, about a mile above 

 the Monte Cristo mine. They belong to the genus Dikelocephalus and 

 resemble closely Dikelocephalus minnesotensis of the Potsdam forma- 

 tion. From analogy with other sections Mr. Emmons thinks it safe to 

 assume that the fossiliferous shales occur above the main body of 

 quartzite and near the base of the transition series. 7 



'Op. cit.,p.209. 



2 Report on Middle Division. (Stratigraphy-Paleozoic formations). TJ. S. Geol. and Geog. Survey of 

 the Terr., Ann. Rep. for 1874, 187G, pp. 110, lil. 



3 Hague, Arnold, and S. F. Emmons. Descriptive geology U.S. Geol. Expl. of the Fortieth Far.; 

 Clarence King, vol. 2, 1877, p. 29. 



4 Report of F. M. Eudlich, geologist of the White River Division. U. S. Geol. Surv. of the Terr., 

 10th Ann. Rep., 1878, p. 130. 



* Geology and mining industry of Leadville, Colorado. Mon. U. S. Geol. Survey, vol. 12, 1886, p. 55. 



• Op. cit. , p. 57. 7 Op. cit., p. 60. 



