1^818.) ON THE FORMATION OF ROCKS. 275 



'# 

 ing small plates of clay slate often disseminated, &c. 



&c. 



26. Gypsum of transition, having a small granular crys- 

 tallization, accompanied with small plates of slate or 

 shist. 



27. Micaceous Slate of transition, alternating with small 

 grained crystalline limestone: the strata consisting of 

 a species of talcy or mica slate, and a variety of shis- 

 toze, intermediate rocks, as on the Ardennes, and the 

 Appenines, including roofing slate, and its attendants. 



28. Anthracite including the attendant strata of clay 

 slate, allum slate, black chalk, Sec. Sec. 



29. Siliceous shist^ as Kiezel-sheiffer, Jasper, and other 

 siliceous stratifications. 



The above rocks are generally stratified, dipping or 

 inclining from, the horizon, at an angle of from 30 to 50 

 degrees, and in some cases even more; most of them, ex- 

 cept perhaps the last, (No. 29,) have been found to con- 

 tain the remains of organic matter, though in small quan- 

 tities; and are a little further removed from the 1st order, 

 though still united by the chain of probable analogy to 

 the same formation. No. 29 approaches nearer the Green 

 stones and Porphyries, where the analogy is not so con- 

 clusive. 

 Greenstone^ including greenstone porphyries, and the 



hard, compact rocks on the borders of the 2d class. 

 Porphyries^ crystals of quartz, feldspar, &c. in compact, 



and often small crystalline bases; found near to the 



limits of the 1st and 2d class, and partaking of .iie 



properties of both. 



As the above rocks approach those of the 2d class, 

 they gradually remove from any positive analogy to the 



