OF THE EARTH. 457 



geological, not in a mathematical sense, has been 

 generated during one period of repose in the form 

 and place of the waters under which it was produced. 

 Where, on the contrary, the positions of approx- 

 imate strata cease to be parallel, or where they must 

 be considered as reversed, in a geological sense, it 

 has also been inferred that an interval, or interrup- 

 tion, of greater or less duration, took place between 

 the deposition of the inferior and that of the superior 

 series; however impossible it may be to conjecture 

 its extent, or to prove the exact nature of the inter- 

 ruption. In most cases, at least, it is further con- 

 cluded, from appearances which I need not now re- 

 peat, that the inferior series was indurated to the 

 state of a rock, before the deposition of the loose ma- 

 terials, destined to be similarly indurated at a sub- 

 sequent period, commenced. It is further evident, 

 that as the inferior strata, like the superior, must 

 have been deposited in a position, horizontal or 

 nearly so, their present state must have been the 

 result of some disturbing force: and if, to simplify 

 this general view, it is assumed that the upper series 

 is horizontal, and the inferior elevated to some con- 

 siderable angle, the same reasoning will apply, under 

 the necessary modifications, to cases where the in- 

 ferior strata are not at a high angle and the superior 

 not at a low one ; because the first change of posi- 

 tion, which involved only the inferior strata, may 

 have been followed by others which affected both ; 

 a supposition proved by a variety of facts already 

 mentioned, which will necessarily be again noticed 

 here. 



Thus, an interval of time, including a disturbance, 

 is proved by every reversal of the positions of approxi- 



