50 



THE EARTH FARMED. 



West of England. The vast thickness of these beds, in 

 some instances, is what attests the profoundness of the 

 primeval oceans in which they were formed ; the Pennsyl- 

 vanian grawacke, a member of the next highest series, is 

 not less than a hundred miles in direct thickness. We 

 have also evidence that the earliest strata were formed in 

 the presence of a stronger degree of heat than what ope- 

 rated in subsequent stages of the world, for the laminse 

 of the gneiss and of the mica and chlorite scists are con- 

 torted in a way which could only be the result of a very 

 high temperature. It appears as if the seas in which 

 these deposits w T ere formed, had been in the troubled state 

 of a caldron of water nearly at boiling heat. Such a con- 

 dition would probably add not a little to the disintegra- 

 ting power of the ocean. 



The earliest stratified rocks contain no matters which 

 are not to be found in the primitive granite. They are the 

 same in material, but only changed into new forms and 

 combinations ; hence they have been called by Mr. Lyell, 

 metamorphic rocks. But how comes it that some of them 

 are composed almost exclusively of one of the materials of 

 granite; the mica schists, for example, of mica — the 

 quartz rocks, of quartz, &c. ? For this there are both 

 chemical and mechanical causes. Suppose that a river 

 has a certain quantity of material to carry down, it is evi- 

 dent that it will soonest drop the larger particles, and 

 carry the lightest farthest on. To »uch a cause it is owing 

 that some of the materials of the worn-down granite have 

 settled in one place and some in another.* Again, some 

 of these materials must be presumed to have been in a 

 state of chemical solution in the primeval seas. It would 

 be, of course, in conformity with chemical laws, that cer- 

 tain of these materials would be precipitated singly, or in 

 modified combinations, to the bottom^ so as to form rocka 

 by themselves. 



The rocks hitherto spoken of contain none of those 

 petrified remains of vegetables and animals which abound 

 so much in subsequently formed 1 ocks, and tell so won- 

 drous a tale of the past history of our globe. They sim- 

 ply contain, as has been said, mineral materials derived 

 from the primitive mass, and which appear to have been 

 formed into strata in seas of vast depth. The absence 

 from these rocks of all traces of vegetable and animal lifr> 

 * Delabeche's Geological Researches. 



