254 



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lystematic, but not very correct designation of transition t jlutz 

 or secondary, and tertiary formations. If the erupted rocks 

 had not exercised an elevating, and, owing to the simultane- 

 ous shock of the earth, a disturbing influence on these sedi- 

 mentary formations, the surface of our planet would have 

 consisted of strata arranged in a uniformly horizontal direc- 

 tion above one another. Deprived of mountain chains, on 

 whose declivities the gradations of vegetable forms and the 

 scale of the diminishing heat of the atmosphere appear to be 

 picturesquely reflected furrowed only here and there by val- 

 leys of erosion, formed by the force of fresh water moving on 

 in gentle undulations, or by the accumulation of detritus, re- 

 sulting from the action of currents of water continents would 

 have presented no other appearance from pole to pole than 

 the dreary uniformity of the llanos of South America or the 

 steppes of Northern Asia. The vault of heaven would every 

 where have appeared to rest on vast plains, and the stars to 

 rise as if they emerged from the depths of ocean. Such a 

 condition of things could not, however, have generally pre- 

 vailed for any length of time in the earlier periods of the 

 world, since subterranean forces must have striven in all ep- 

 ochs to exert a counteracting influence. 



Sedimentary strata have been either precipitated or depos- 

 ited from liquids, according as the materials entering into 

 their composition are supposed, whether as limestone or ar- 

 gillaceous slate, to be either chemically dissolved or suspend- 

 ed and commingled. But earths, when dissolved in fluids 

 impregnated with carbonic acid, must be regarded as under- 

 going a mechanical process while they are being precipitated, 

 deposited, and accumulated into strata. This view is of some 

 importance with respect to the envelopment of organic bodies 

 in petrifying calcareous beds. The most ancient sediments 

 of the transition and secondary formations have probably been 

 formed from water at a more or less high temperature, and 

 at a time when the heat of the upper surface of the earth 

 was still very considerable. Considered in this point of view, 

 a Plutonic action seems to a certain extent also to have taken 

 place in the sedimentary strata, especially the more ancient*; 

 but these strata appear to have been hardened into a schistose 

 structure, and under great pressure, and not to have been 

 solidified by cooling, like the rocks that have issued from the 

 interior, as, for instance, granite, porphyry, and basalt. By 

 degrees, as the waters lost their temperature, and were able 

 lo absorb a copious supply of the carbonic acid gas with which 



