ON STRATIFICATION. 



phyiy series. But these strata- seams are almost 

 always parallel with the slaty structure of the 

 rock, so that, when they disappear in slaty rocks, 

 the direction and dip of the rock may be ascer- 

 tained by attending to the position of the slaty 

 structure. It would appear from this statement^ 

 that the seams of the strata are in many cases to 

 be viewed as particular separations effected in the 

 crystallizing substance, of the same nature, but 

 on a larger scale, than the seams in the distinct 

 concretions, or the laminae of the slaty struc- 

 ture ^. 



2. In primitive country, an uninterrupted tran- 

 sition is to be observed from granite to clay-slate, 

 in such a manner that the great masses are to be 

 .considered as principal formations, and the smaller 

 as subordinate formations ; and these are so con- 

 nected by intermixture and gradations, that w^e 

 can say of any two contiguous portions of rock, 

 whether separated by strata-seams or not, that 

 they are of cotemporaneous formation ; thus, any 

 two contiguous portions of granite, of gneiss, or 

 of gneiss and granite, or of gneiss and mica-slate, 

 are of cotemporaneous formation. 



* In horizontal strata of sandstone and*other rocks, we some- 

 times observe the slaty structure at right angles to the direction 

 of the stratum : if, then, the slaty structure, and the strata seams 

 are but varieties of the same character, it follov/s, that vertical 

 strata have not been in general elevated into their present situa-» 

 tion by a force acting after their formation^ but are in their ori=. 

 g;inal position. 



