116 ARRANGEMENT OF THE STRATA. 



genera and species. The mountain limestone, with some 

 beds of shales, sandstones, and imperfect coal. 



IX. THE DEVONIAN G-ROUP. A marine formation ; con- 

 sisting of red and green marls, concretionary limestones, 

 called cornstones, conglomerate, tilestone, micaceous and grey 

 sandstones, green slates, and sandstone, and blue crystalline 

 limestone, containing corals, mollusca, and fish. 



X. THE SILURIAN GROUP. An extensive series of marine 

 deposits; comprising limestones, sandstones, grits, flag-stones, 

 shales, and slates, containing corals, mollusca, Crustacea 

 (trilobites), and fish. 



XI. THE CAMBRIAN G-ROTTP. A marine formation, com- 

 prising vast beds of slate rocks, with dark-coloured lime- 

 stones, and sandstones, containing two or three species of 

 corals, and of brachiopodous mollusca. 



XII. THE CUMBRIAN G-ROUP. A like extensive series of 

 deposits, obviously of sedimentary origin, but in which no 

 organic remains have been discovered. 



THE PRIMARY STRATA. 



XIII. THE MICA-SCHIST. Composed of mica and quartz, 

 interlaminated so as to present the appearance of stratifi- 

 cation, but containing no organic remains. 



XIV. THE GrNEiss. Formed of the component parts of 

 granite; mica, quartz, and feldspar, fine-grained and lami- 

 nated, so as to present the appearance of having been pro- 

 duced by the abrasion of granite, and then deposited in 

 water. Both the gneiss and mica-schist are supposed to 

 have been altered by heat, subsequently to their deposi- 

 tion. 



THE PLUTONIC, OR UNSTRATITTED PRIMARY ROCKS. 



XV. THE GTRANITE AND TRAPPEAN BOCKS. Comprising 

 granite, syenite, greenstone, hornblende, diallage, serpentine, 

 &c. ; together with basalt, porphyry, clinkstone, claystone, 

 and the trap rocks, the whole being alike destitute of strati- 

 fication and of organic remains. 



The relative thickness of each of these several deposits 



