512 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



U. S. Geological Survey of the Territories, 18G7, 18G8,and 1869, [1873,] 

 p. 79.) 



Ill the Report of the XJ. S. Geological Survey of Colorado and New 

 Mexico, 1869, (pp. 22, 73, 87,) and in the publication last mentioned 

 above (pp. 122, 173, 187), Dr. Hayden presents a clear statement of 

 his views regarding the supposed Laurentian rocks in the region ex- 

 amined by him. He gives, however, no evidence in support of these 

 views. It is simply a profession of faith, in the following words : — 



" I have assumed the position that all the rocks of the West are, or were, 

 stratified, and that where no lines of stratification can be seen, as in some of 

 the massive granites, they have been obliterated by heat during their meta- 



morphism This iron occurs in the gneissoid rocks, or what is called 



the Laurentian group, to which group, I believe, all the gneissic and perhaps 

 the entire mass of metamorphic rocks of the Eocky Mountain system belong. 

 I have assumed the position, m all my investigations, that there are but two 

 classes of changed rocks in the West, viz., igneous and metamorphic, and that 

 the oldest granites which form the nuclei of the loftiest mountain ranges w^ere 

 once aqueous rocks, deposited in the same manner as the limestones or sand- 

 stones of our most modern formations The gold and silver lodes of this 



Territory [Colorado], so far as they are observed, are entirely composed of the 

 gneissic and granite rocks, possibly rocks of the age of the Laurentian series of 

 Canada." 



On the same page from which the last remark is copied, Dr. Hayden 

 distinctly shows that he regards the foliation of gneissoid rocks as sy- 

 nonymous with bedding and stratification. Had all our geologists been 

 as frank regarding the theoretical views upon which their work is based, 

 it would be far easier to estimate the value of their observations. 



In the Annual Report for 1870 the same view of the age of the rocks 

 in the valley of the Chugwater was repeated. Of the rocks on the 

 north side of the Uinta Range, near the head-waters of Bear River, Dr. 

 Hayden remarks : — 



" In all this series of strata, from the red beds to the oldest quartzites, I was 



able to detect no unconformability I am inclined to believe that the 



upper beds are Silurian, that they pass gradually down without any break in 

 the sequence of time to rocks of Huronian age. The purplish quartzites are 

 almost precisely like those which occur at the Sioux Falls in Dakota, and at 

 the Pipestone quarry, in color and texture, which Professor Hall regards as 

 Huronian age." (I. c, pp. 14, 50.) 



The above quartzite appears to be the Weber quartzite (Carbonif- 

 erous) of the Fortieth Parallel Survey, and the Uinta sandstone (Devo- 

 nian) of Major Powell (Systematic Geology, p. 152 ; Geology of the 



