154 ON THE CHARACTERS AND DISPOSITION 



stitution of granite, which prove that it has, for a 

 longer period, been under the influence of heat than 

 the trap rocks. This is its more perfect and distinct 

 crystallization ; a difference which we are enabled to 

 produce, even in our laboratories, by prolonging the 

 fluid state of fused traps, and which is a common oc- 

 currence in volcanic rocks under similar differences in 

 the rapidity of cooling. J shall hereafter also attempt 

 to show, that gneiss itself is the evanescent limit 

 between granite and the other stratified rocks. Thus 

 it is at least possible, perhaps even probable, that in 

 many cases where granite has actually been erupted, 

 the rocks which it covered have, by long exposure to 

 its action and by being thus involved in it, been con- 

 verted into its substance. This supposition is not in 

 want of support from analogies furnished by the 

 Trap rocks ; as an instance occurs in Canty re, as 

 well as on the continent of Europe, where the gradual 

 conversion of a schistose rock into porphyry, under 

 similar circumstances, is proved in the most unques- 

 tionable manner. 



In the next place, we may apply to granite as we 

 now find it, the cases of apparently unerupted trap 

 already examined. The immense deposits of mate- 

 rials which now form the alluvial tracts of the globe, 

 the enormous masses of secondary strata which have 

 been produced by antient materials of the same 

 nature, all prove the magnitude of the destruction 

 which mountains have formerly experienced, which 

 they are now daily undergoing. Let imagination re- 

 place the plains of Hindostan on the Himalya, or 

 rebuild the mountains which furnished the secondary 

 strata of England, and it needs not be asked what is 

 the extent of ruin, modern or antient. In this ruin, 

 the highest rocks participate most largely ; so largely, 



