ON GEOLOGr. 



59 



6\in mequaiity of thickness in different places, and partly from other causes, 

 the continuity is often interrupted — yet still we trace enough of it to con- 

 vince us that the rocks which constitute the crust of the earth, when con- 

 templated upon a large scale, are every where the same, and that they in- 

 variably occupy a like situation with respect to each other. 



The labours of Mr. Kirwan and M. de Saussure gave the earliest hints 

 upon this subject ; and the geological theories of Professor Werner of 

 Freyburg, and of M. de Cuvier of Paris, are entirely founded on the same. 

 These theories, though derived in some measure from different sources of 

 mineralogical study, coincide not merely in their general outhne, but in all 

 their more prominent parts, and only differ in their mode of accounting for 

 the more limited or local deposites. 



M. Werner, "from whom alone," to adopt the language of M. de Cuvier, 

 " we can date the commencement of real geology," so far as respects the 

 mineral natures of the strata, divided, in his first view of the subject, all the 

 various rocks that enter into the solid crust of the earth into five classes. 



Of these the first class consists of those rocks which, if we were to 

 suppose each layer to be extended over the whole earth, would lie lowest, 

 or nearest the centre, and be covered by all the rest ; it comprises seven 

 distinct sets, as granite, gneiss, mica-slate, clay-elate, a pecuhar kind of 

 porphyry, sienite, and a pecuhar kind of serpentine. Of these, granite lies 

 the undermost, and sienite the uppermost ; and in the midst of several of 

 them we meet with beds of not less than eight other kinds of rock, as 

 though dropped into them by accident — as topaz, another kind of por- 

 phyry, serpentine, limestone, flint-slate, and trap, quartz, and gypsum ; 

 which are hence called subordinate rocks of this class, and which extend 

 the whole number of sets belonging to it to fifteen. 



These are supposed to have been earliest produced, and when the earth 

 first emerged from a state of chaos to a state of order ; and are hence 

 denominated primitive formations. They are distinguished by the fol= 

 lowing character. Not a single rehc of either animal or vegetable petri- 

 faction is to be found in any of them. The lowermost or older contain 

 no carbonaceous matter ; which is discoverable but .very sparingly in the 

 superior or newer. They are all chemical combinations, and generally 

 crystallized ; the crystallized appearance being most perfect in the oldest, 

 and gradually becoming less perfect in the newer formations. I have 

 already observed that the whole of this scale of formation does not regularly 

 coat the nucleus of the earth ; so httle so, indeed, that sometimes even the 

 granite itself, the lowermost rock of all, is left bare, and not pressed down 

 or coated by a deposite of any other kind of rock : and so of the rest. 

 Wherever this deficiency takes place, the rock thus left at hberty rises 

 uniformly higher than it is found to do where pressed upon and invested 

 with its common coatings. But every rock does not, under such circum- 

 stances, 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 lefl 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 re- 



