GEOLOGY. 295 



PALEOZOIC ROCKS. 



The thickness of the Lower Paleozoic rocks of Northwest- 

 ern Georgia, supposed by Bradley to be the equivalents of 

 the crystalline belt of the Blue Ridge, is, according to Little, 

 as follows : Above the Ocoee slates and conglomerates, which 

 are of great and uncertain volume, and perhaps correspond 

 to the Taconian (Lower Taconic, Emmons), is the Chilhowee 

 sandstone, considered the equivalent of the Potsdam, and 

 2000 feet in thickness, followed by the Knox group of lime- 

 stones, sandstones, and shales, regarded as the representa- 

 tives of the Calciferous sand-rock and the Quebec group, and 

 measuring 4400 feet. To these succeed the Chazy limestone, 

 600 feet ; the Trenton limestones and shales, 700 feet ; and the 

 Cincinnati group, consisting of silicious limestones and shales, 

 including layers of red hematite, from 200 to 400 making in 

 all about 8000 feet from the base of the Potsdam. 



Linnarsson, in the Swedish Paleozoic series, follows Belt, 

 Lyell, and Hicks in giving the name of Lower Cambrian to 

 the Paradoxides schists and the fossiliferous sediments be- 

 low them (the whole being equivalent to the Lower Cambrian 

 of Sedgwick), and that of Upper Cambrian to the succeed- 

 ing Dictyonema and Olenus schists, which together are the 

 representatives of the Lingula flags, and perhaps of the lower 

 division of the Tremadoc, its upper division being represent- 

 ed by the Ceratopyge limestone, which is immediately over- 

 laid by the Lower Graptolitic schists, the equivalent of the 

 English Arenig or Skidclaw group. This is, by the authors 

 named, included, together with the succeeding Bala group 

 (Llandeilo and Caradoc), in the Lower Silurian (the Upper 

 Cambrian of Sedgwick), to which, according to Linnarsson, 

 the fauna of the Upper Tremadoc is more nearly related than 

 to the underlying divisions. The strata which by Hunt and 

 others have been called Siluro-Cambrian, or Cambro-Silurian, 

 in North America, include only the Bala group (Trenton and 

 Cincinnati), for the reason that the Arenig (represented by 

 the Phyllograptus shales of Levis) was not recognized in the 

 New York Paleozoic series. Hence the Siluro-Cambrian is 

 not the full equivalent of the Lower Silurian of Linnarsson et 

 al., and of the Upper Cambrian of Sedgwick, whose nomen- 

 clature for these rocks is still retained in its integrity by 



