234 PROCEEDINGS OP THE AMERICAN ACADEMY 



Map of tlie Eureka District accompanying the memoir of Arnold 

 Hague shows the " Eureka quartzite " either seeming to oveHap, or 

 lying in direct contact with, all the different groups of Primordial, 

 except the "Secret Canon shale," which can only be explained by a 

 transgressive discordance or a dilFerent geographical distribution of the 

 level of the sea. It is probable that the great break of the Green 

 Mountains, the most important as breaking and dislocation of strata 

 that has ever happened in North America, was felt in its effects in this 

 Nevadian fiord of the Upper Taconic by a slight change in the level 

 of the sea, sufficient to produce a geographical distribution special and 

 peculiar to the deposits of sand which form the " Eureka quartzite." 



In order to show the numerous points of resemblance and the multi- 

 ple relations existing between the "Eureka quartzite" and the "Red 

 Sandrocks" or " Potsdam sandstone" of Vermont, New York, and the 

 Grand Canon of Arizona, I will add that there has been at Eureka 

 a break between the quartzite and the following formation, the " Lone 

 Mountain limestone." An unconformity exists between the two for- 

 mations, and a denudation or erosion has destroyed the upper part of 

 the " Eureka quartzite." As we know now that it is the upper part 

 of the Potsdam which contain fossils, the lower having furnished in 

 all America but six or eight species, we can understand why no fossils 

 have yet been met with in the quart zites occupying the place of the 

 " Potsdam sandstone " at Eureka. 



The "Taconic System" in Nevada is finished with the "Eureka 

 quartzite." The second fauna is above, analogous to that of the 

 " Champlain division " of Emmons, and the " Lone Mountain lime- 

 stone," from 1,800 to 2,000 feet thick, represents the true " Cam- 

 brian," from the " Calciferous," " Chazy," and "Trenton," even to the 

 " Utica " and " Lorrain shales." It is nearly double the thickness of 

 the typical series of New York. 



Messrs. "Walcott and Hague make one system only of the five lower 

 divisions, "Prospect Mountain quartzite and limestone." "Secret 

 Canon shale," and " Hamburg limestone and shale," they call "Cam- 

 brian." Then uniting the " Pogonip limestone" with the "Eureka 

 quartzite " and the " Lone Mountain limestone," they have made a 

 second system of 5,000 feet, which they call " Silurian." It is an 

 entirely palaiontological classification, which follows only uniformist 

 preconceived opinions. It pays no attention to discordances of stratifi- 

 cation, nor to I'rimordial forms, especially the Primordial species, 

 some of which are found from " JProspect Mountain " to " Pogonip 

 limestone," such as Lingula manticula and Crepicephalus Galuti- 



