HAYDEN'S SURVEY. 513 



Uinta Mouutains, p. 70). Hence, as it appears, considerable difference 

 of opinion exists as to its age. Mr. S. F. Emmons apparently inclined 

 tt> regard it as Cambrian (Descriptive Geology, p. 199), while Professor 

 Marsh and Dr. C. A. White thought it probable that it was Silurian 

 (Am. Jour. Sci., 1871, (3) I., p. 193 ; Annual lleport, 187G, p. 23). In 

 his Annual Report for 1871, (p. 39,) Dr. Hayden remarked : — 



" The precious metals, as gold and silver, are found, so far as my observa- 

 tions have extended, entirely in the metauiorphic rocks which hold a position 

 below all groups of strata that we have been iu the habit of regarding as Pale- 

 ozoic. Whether they belong to the series denominated in Canada the Iluronian 

 or Laurentian, we have no data to decide positively ; but inasmuch as they are 

 all clearly stratified rocks, they are plainly of sedimentary origm." 



In the Report for 1873, Dr. Hayden stated that 



" the underlying metamorphic rocks [near South Park] are made up in part of 

 quartzitic sandstones, full of rounded pebbles of quartz, which would indicate 

 that they might belong to the Laurentian series." (I. c, p. 41.) 



In the Report for 1874, (pp. 190, 191, 239,) Dr. F. M. Endlich held 

 that the granite and other so-called metamorphic rocks were formed 

 from the metamorphosis of the Silurian and Devonian rocks in the dis- 

 trict studied by him.* These rocks appear to be the same as those 

 called Archaean by the other members of the Survey. (See also Report 

 for 1875, p. 113.) 



In the Annual Report for 1875, Dr. A. C. Peale makes the following 

 statement : — 



" Sufficient data have not yet been obtained to determine the exact age of the 

 metamorphic series, although, as Mar\dne remarks of those farther east, [An- 

 nual Report, 1873, p. 139,] ' the prevalence of siliceous and granitic types recalls 

 the descriptions of Laurentian areas.' In one place the schists are very dis- 

 tinctly stratified, consisting of dark micaceous schists, with seams of quartz 

 and feldspar. These may be of Huronian age, although we cannot trace their 

 relations to those of the other Arehsean rocks, as they are exposed in an isolated 

 area at the bottom of canons distant from the other outcrops." Q. c, p. 64.) 



In the Annual Report for 1877, (p. 156,) Dr. F. M. Endlich, in a 

 tabular view of the formations of the Sweetwater district, divides the 

 Azoic rocks into three systems. The oldest of these, called Prozoic, 

 consists of massive granite. The third, called Huronian, likewise con- 

 sists of granites, less massive than those of the first system, and con- 



* The area between the meridians of 107° and 108°, and the parallels of 37° 15' 

 and 38° 15^', at the head of the Rio Grande and the Rio Animas. 

 VOL. VII. NO. 11. 33 



