Ch. XIII.] THE INCLINED POSITIONS OF STRATA. 267 



removed by aqueous denudation. But, at the same time, it 

 must be confessed that this is a mere attempt to put aside a 

 difficulty which a better knowlege of geological phenomena 

 may hereafter satisfactorily explain : in the interim, however, 

 it must equally remain a stumbling-block for the Plutonic 

 theory ; for although the central fire is fully adequate to such 

 an elevation, yet the how and the when, in this case, are not 

 clearly indicated. 



In thus contending that many, and indeed far the greater 

 number of, inclined strata are in their original position ; it is 

 not disputed that the convulsions, produced by the internal 

 fire, may have occasioned many dislocations and displace- 

 ments. 



Before proceeding, however, farther in the examination of 

 this question, it is time to enquire into the nature of this 

 igneous agency, as regards its power of effecting an elevation 

 of the strata. 



The phenomena of active volcanos afford presumptive 

 evidence that there is an internal fire, as supposed by the 

 prevailing theory, by the expansive force of which the rocks, 

 being in a state of igneous fusion, are either injected from 

 time to time amongst the strata, or are poured out through 

 the fractured strata on the surface of the earth, either under 

 water, or in contact with the atmosphere. And it has been 

 inferred, since some of the lavas so formed cannot be dis- 

 tinguished from greenstone, and other rocks, which are most 

 intimately and inseparably connected with granite, that, 

 therefore, the latter rock is of igneous origin, and that the 

 strata have been ruptured and tilted up by its protrusion in a 

 melted or solid state. 



In the first place, as regards the analogy of primary horn- 

 blende rocks and lavas, we think that their perfect resem- 

 blance, both in composition and structure, does not indis- 

 putably prove that they were formed in the same manner. 

 It is true that lava may be converted into greenstone, and 

 the latter into the former, by duly regulating the mode of 



