ON GEOLOGY. 



not, under such circumstances, rise equally high, or with an equal degree of / 

 freedom ; for granite rises highest of all ; and hence we frequently find it 

 composing the tops of our loftiest chains of mountains, as well as the basis 

 of the earth's solid crust. It forms the great body of the Swiss mountains 

 and the Alps, though gneiss is here also found in great abundance. 



The level of gneiss, when left at equal liberty, is a little lower than that of 

 granite. It constitutes the vast mass of the Carpathian mountains, that 

 divide Transylvania and Hungary from Poland. 



The level of mica-slate is lower than that of gneiss, and the level of clay- 

 slate lowest of all. So that there is a regular sinking of these respective 

 levels from granite to clay-slate : while the newer porphyry and sienite are 

 often laid over their summits, as though these two formations had been de- 

 posited long after the production of the others; an idea which is still farther 

 strengthened by our meeting occasionally with a bed of breccia, or pudding- 

 stone, composed of fragments of the older or lower rocks, capping the gneiss, 

 granite, or other formation before the porphyry or sienite has been deposited. 



The SECOND CLASS of rocks, or that which, when the number of coatings is 

 complete, lies immediately over the preceding, consists of gray-wacke slate, 

 and a peculiar kind of limestone, greenstone, and amygdaloid ; together with 

 subordinate masses of the proper primitive formations, sienite, porphyry, and 

 granite ; as though some portions of these had become crystallized after the 

 rest, along with the next layers in succession, or had been separated from the 

 parent rocks by some early commotion. Gray-wacke, which is a concrete 

 term, denoting a conglomerate rock of a peculiar kind, having a basis of clay- 

 slate, and being studded or otherwise intersected with portions of quartz, fel- 

 spar, and scales of mica, may be exemplified by what m Cornwall is called 

 killas, a far more euphonous word ; and hence gray-wacke and gray-wacke 

 slate may be distinguished by the terms amorphose and schistose killas. The 

 Cornish killas lies directly over the granite of that county, which possesses 

 the character ascribed by Werner to granite of the highest antiquity.* 



These formations, for the most part, irregularly alternate with each other, 

 instead of preserving one regular and successive order, as the different sets 

 of the primitive formations do; excepting that the limestone appears usually 

 undermost, and placed, as the basis of the rest, upon the sienite or uppermost 

 of the first class. It is in this second class of formations that petrifactions 

 first make their appearance; and it deserves particular attention that they are 

 uniformly confined, both in the animal and vegetable kingdoms, to those of 

 the lowest links in the scale of organization ; and even among these to spe- 

 cies which are at present altogether unknown, and which appear therefore to 

 be totally extinct. Thus the animal petrifactions consist entirely of ammo- 

 nites, mytilites, unknown corals, and other zoophytic worms ; and the vege- 

 table petrifactions of reeds, ferns, and other palm-like plants, mosses, and 

 other cryptogamic productions, which occupy the lowest part in the scale of 

 vegetable life, as zoophytic worms do among animals. It is here, also, that 

 carbonaceous matter, which is chiefly of vegetable origin, first makes its ap- 

 pearance in any considerable quantity. 



To this class of rocks, therefore, M. Werner has given the name of transi- 

 tion formations; as believing them to have been produced while the earth 

 was in a state of transition from inorganic matter to organic life, — from an 

 uninhabited to an inhabited condition. The date of their formation, however, 

 is proved even from their natural appearance, to have been very remote ; 

 since, as already observed, the whole of the petrifactions which they contain 

 consist of plants and animals, not only of the very lowest species, but which 

 now seem to be altogether extinct. 



The TmRD class of rocks is denominated floetz, that is, flat or horizon- 

 tal formations, in consequence of their usually appearing in beds much 

 more nearly horizontal than the preceding. They lie immediately over the 

 transition-class, and consist of the twelve following distinct sets of rock, each 



* See Allan's reiyiarks on the transition-rocks of Werner, in Thomson's Annals of Piulos. vol. iii. p. 23 

 Compare with Jameson's definition of the same. Id. Feb. 1817, p. 17. 



