516 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



than a certain similarity to that formation in lithokigical characteristics. Their 

 position upon the stratigraphic chart is, therefore, entirely provisional." (I. c, 

 p. lOG.) 



POWELL'S SURVEY. 



In the publications of the U. S. Geographical and Geological Survey, 

 under Major J. W. Powell, we are able to find but little relating to the 

 subdivision of the supposed Azoic rocks examined by that Survey. 



In a " Report on the Geology and Resources of the Black Hills of 

 Dakota," by Henry Newton and Walter P. Jenney, published in con- 

 nection with Major Powell's Survey, and revised by Mr. G. K. Gilbert, 

 the granite is shown to be eruptive along the foliation of the schist, and 

 not a sedimentary rock. An attempt is made to divide the rocks of the 

 region into two ages, Laureutian and Huronian ; but they do not aj^pear 

 lithologically to have the characters of either formation. The division 

 into two groups is stated to be a lithological one only, as the two series 

 conform in strike, A diversity of dip is said to have been observed at 

 one point,, but that observation is not insisted upon. 



Furthermore, however, we find it stated that " the lithological evi- 

 dence fails to give even its feeble support to the theory that the two 

 Archaean groups of the Black Hills are the representatives of the two 

 Archaean gi'oups of Canada." (l. c, pp. 45-80.) 



CALIFORNIA. 



The geological investigations of the California Survey, carried on from 

 1860 to 1874, show that the gold-bearing slates of the Sierra Nevada 

 are of Jurassic and Triassic age. No fossils older than the Carbonifer- 

 ous have ever been found in that range. The Mesozoic series has been 

 uplifted by eruptive granite, which forms the axis of the chain. On 

 these uplifted rocks strata of the Cretaceous epoch rest unconformably 

 and almost without disturbance. Hence it is a well-established fact — 

 the geological age of the different formations having been made out by 

 the discovery of fossils at numerous localities, and reference to their 



