284? DISCOURSE ON THE hTUDY 



thus wonderfully preserved (like ancient medals and 

 inscriptions in the ruins of an empire), afford a sort 

 of rude chronology, by whose aid the successive de- 

 positions of the strata in which they are found may 

 be marked out in epochs more or less definitely 

 terminated, and each characterized by some pe- 

 culiarity which enables us to recognise the deposits 

 of any period, in whatever part of the world they 

 may be found. And, so far as has been hitherto 

 investigated, the order of succession in which these 

 deposits have been formed appears to have been 

 the same in every part of the globe. 



(318.) Many of the strata which thus bear evi- 

 dent marks of having been deposited at the bottom 

 of the sea, and of course in a horizontal state, are 

 now found in a position highly inclined to the ho- 

 rizon, and even occasionally vertical. And they 

 often bear no less evident marks of violence, in 

 their bending and fracture, the dislocation of parts 

 which were once contiguous, and the existence of 

 vast collections of broken fragments which afford 

 every proof of great violence having been used in 

 accomplishing some at least of the changes which 

 have t^ken place. 



(319.) Besides the rocks which carry this in- 

 ternal evidence of submarine deposition, are many 

 which exhibit no such proofs, but on the contrary 

 hold out every appearance of owing their origin to 

 volcanoes or to some other mode of igneous action ; 

 and in every part of the world, and among strata 

 of all ages, there occur evidences of such action so 

 abundant, and on such a scale, as to point out the 

 volcano and the earthquake as agents which may 



