414 NATURAL HISTORY. 



rEiffel, Strigocephalus, and Cornita marbles. The lower 

 section, which is made up of Graywacke, Clay Slate, 

 Sandstone, and Limestone, also composes the principal 

 feature of the old carboniferous deposits found in the 

 Graywacke and Clay .Slate formations of the Rhenish 

 territory, so rich in the fossil remains of the oldest times, 

 and called the Paleozoic formation, are found in various 

 strata in the Eiffel, Ardennes, and Maas region. In 

 Sweden, where this formation also exists, are found lay- 

 ers of Alum Slate and Bituminous Shale, alternated with 

 banks of Swinestone, more generally termed fetid lime- 

 stone. In England this formation is particularly ex- 

 tensive. The lowest section of the Silurian system are 

 the rocks which form 



The Cambrian or Schistose System, and are the 

 lowest sedimentary deposits known. The first stratum 

 consists of Graywackes, Schistose Clay, Conglomerates (a 

 rock composed of pebbles), and dark Limestone. The 

 Clay Slate rocks are hard, dark -colored, and split easily, 

 therefore are used in place of shingles for roofing ; coral- 

 lines and fucoides are occasionally present. The Gray- 

 wacke slate is firm but very coarse-grained, occasionally 

 laminate, enclosing fragments of clay slate. This system 

 of strata is developed on a grand scale, extending many 

 thousand feet in width and thickness. The second stra- 

 tum is composed of Balakalk, which is an argillaceous 

 rock formation made up of dark, thick limestone and 

 clay slate, is of inconsiderable extent or depth, and con- 

 tains but few fossil remains, which are those of the Tere- 



* Receives its name from the Siluri, the ancient Britons, who in- 

 habited the region where these strata are most distinctly developed, 

 and is next above the Cambrian, -which is so called from Cambria, the 

 original name of Wales. 



