THEORY OF THE EARTH. 413 



aspect of these rocks; as the latter penetrates and 

 unites with them; depositing also aqueous minerals in 

 their cavities, when these are present. The further 

 action of these powers decomposes and disintegrates 

 them ; while, under each form, and, in the latter, under 

 fragments of various sizes, they become moved by gra- 

 vity and the flow of water, forming alluvia, on the sur- 

 face of the earth, and beneath the waters: the latter 

 constituting strata, which according to various circum- 

 stances, differ, and form successions, in parallel order. 



All this, which occurs now, has also occurred 

 formerly; and thus too, as such strata are now consoli- 

 dated into rocks, so have they been similarly consoli- 

 dated in former times. They are now consolidated by 

 solutions of earths in water, by pressure, and by heat; 

 and thus have they been consolidated at distant pe- 

 riods. Lastly, such consolidated strata, or rocks, 

 have been subjected to the same chemical and mecha- 

 nical actions as the igneous rocks? and they have, in 

 the same manner, furnished materials for alluvial strata, 

 separately, or in combination with those. 



Wherever heat has demonstrably acted on strata 

 consolidated by water and pressure, or, possibly, by a 

 small degree of heat, their chemical and mineralogical 

 characters are changed: and the peculiar differences 

 between the more antient and the more recent strata, 

 are therefore attributed to this cause, as operating 

 through the igneous rocks: the more antient stratum 

 being the lowest, and the more recent the highest, in 

 geological position. And under the extreme effect of 

 such heat, in peculiar circumstances, such a stratum 

 may become an unstratified rock; because under a 

 similar condition to a stratum fused in a volcano. 

 Whence also, the near resemblance in the mineral 

 characters of certain strata and some unstratified rocks. 



The solid spoils of animals, chiefly marine, consti- 



