512 



THE AZOIC SYSTEM AND ITS SUBBIYISIONS. 



U. S. Geological Survey of the Territories, 1867, 18G8, and 1869, [1873,] 

 p. 79.) 



In the Eeport of the U. S. Geological Survey of Colorado and 'Hew 

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

 above (pp. 122, 173, 187), Dr. Hajdon 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 he seen, as in some of 

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



morphism This iron occurs in the gneissoid roclcs, 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 Kocky Mountain system beloug. 

 I have assumed the position, in all my iuvestigations, tliat there are but two 

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

 the oldest granites which form the nuclei of the loftiest mountain ranges were 

 once mjueous 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 entirel}^ 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 w^hich their work is based, 

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



In the Annual Report for 1870 the sauie view of the ago of the rocks 

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

 north side of the Uinta Range, near the head-waters of Dear 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 Huroniau age. The purplish (juartzites arc 

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

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

 Iluronian age." (/. 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 



