The Cambrian Rocks of North America. 7\) 



This great series, of many thousand feet, which is overlaid uncon- 

 formably by the Cambrian sandstones, and also, according to Ir- 

 ving, by the Keweenian, consists chiefly of quartzites and argillites, 

 with beds of magnetite. The remains of a sponge have been de- 

 tected in a calcareous mass got by the speaker at Thompson, Min- 

 nesota, from the argillites of this series, which, in a late commu- 

 nication to the National Academy of Sciences, he has referred to 

 the Lower Taconic or Taconian horizon. He now stated his con- 

 clusion, drawn from various facts, that, while these Animikie 

 rocks rest unconformably in this region upon the Huronian, the 

 two series have hitherto been confounded under the common 

 name of Huronian. 



[The Cambrian areas of the Atlantic coast, as seen in Massachu- 

 setts, New Brunswick and Newfoundland, not being included in 

 the great North American basin have been omitted in the present 

 notice. As regards the Cambrian of the Cordillera area, the- 

 studies of Arnold Hague and C. D. Wolcott in the Eureka Dis- 

 trict in Nevada, just published in the Third Annual Report of 

 the U. S. Geological Survey, show that the paleozoic column to the 

 top of the coal measures, as there displayed, includes, not less 

 than 30,000 feet, marked by only one stratigraphical break, 

 which occurs in the rocks of the second fauna. The series begins 

 with the Prospect Hill quartzite, which, although its base is not 

 seen, shows a thickness of 1500 feet. This is succeeded by 3000 

 feet of more or less magnesian limestone known by the same local 

 name, followed by the Secret Canon shales, the Hamburg lime- 

 stones and the Hamburg shales, making, in all, a series of nearly 

 8000 feet which are referred to the Cambrian. 



The first organic remains in this series are met with in what 

 are described as the Olenellus shales, which lie between the basal 

 quartzite and its overlying limestones, and contain a fauna closely 

 related to that of the slates of Georgia, in Vermont, called Lower 

 Potsdam by Billings. In the succeeding limestones and slates 

 already named there is found at various horizons an abundant 

 fauna resembling that of the Potsdam of the Mississippi area. 

 We have thus in the Cordilleras, in conformable succession, the 

 Lower and Upper Potsdam divisions of the east. The forms 

 of the first fauna, pass upwards from the Hamburg slates 

 ome distance into the great overlying Pogonip limestone, which 



