40 Dr. Mac Cullocli on the 



Having thus shown the identity of certain varieties of granite, 

 with other rocks appertaining to the trap family, it will be use- 

 ful to place, in a condensed view, those instances already alluded 

 to in the beginning of this paper, where the members of that 

 family present the characters which are most generally found 

 in granite. A few of them have been pointed out in the author's 

 work on the Western Islands, to which allusion has already 

 been made ; but the importance of the subject is such as to 

 demand a more distinct statement of the several facts, while 

 the nature of the present communication affords an opportunity 

 of balancing and comparing them with the analogous pheno- 

 mena described in it. Thus it will more readily be perceived, 

 that whatever resemblance the most ancient unstratified rocks 

 may sometimes bear to the most recent, corresponding examples 

 are not wanting in the latter of a similar resemblance to the for- 

 mer. That this comparison has never yet been distinctly made, 

 or supported by the evidence of facts, will be an additional 

 reason for extending this paper so as to comprise whatever is 

 necessary for that purpose in the history of the trap family. 



In the general, or geological, features of granite and of the 

 trap rocks, tliere are so many points of resemblance that they 

 cannot fail to have attracted the attention of the most ordinary 

 observers. Granite is never stratified, but is found in shapeless 

 masses which are subjacent to all the strata, of whatever anti- 

 quity, near to which they lie. To examine and analyze all the 

 contradictory opinions, which have prevailed on this subject, 

 is here inadmissible ; but it may be remarked, in a general way, 

 that the adduced instances of stratification in granite, may all 

 be referred to the laminar concretionary structure on the large 

 scale ; or are portions of gneiss of which the texture so often 

 becomes perfectly granitic ; or, lastly, are veins of that rock 

 traversing the gneiss in directions parallel to its stratification. 



The trap rocks are also unstratified ; or, in the predominant 

 instances at least, these irregular forms prevail, while the masses- 

 differ from those of granite in being superior to all the rocks 

 which they accompany. Instances of u disposition which has 



