54 Dr. Mac Culloch's Sketch of the 



syenite, I must premise that I have not found in Sky any indication 

 to denote the relative order of the two. If indeed they are both ir- 

 regular substances, as I think there is no reason to doubt, any pri- 

 ority or posteriority is out of the question, or at least it cannot be 

 ascertained by examining their juxtapositions. If the one set were 

 proved to be constantly superior to one set of stratified rocks, and the 

 other to a different and later set, the question of rank might be 

 settled between them : but these connections are difficult to ascer- 

 tain to a sufficient extent, and possibly none such exist. If one stra- 

 tified rock is in one place superior to another, we are sure that it is 

 every where superior ; but if we have ever so clearly proved that a 

 body of trap or of any other unstratified rock is superior and in con- 

 tact in one place to any given stratum, we have no certainty that it Is 

 equally so every where. Thus I shall in this island show that the 

 trap rests in one place on the latest sandstone, in another on the 

 earliest. No means therefore are offered here of determining the re- 

 lative order of these two unstratified rocks, but I have little doubt 

 from the phenomena which I have witnessed in Rum and Mull, that 

 they are both portions of one irregular mass. I shall therefore com- 

 mence with the trap as the most extensive. 



I was once inclined to make a distinction between the trap which 

 forms so large a part of the Cuchullin hills, and that which is found 



class of rocks, it is in no danger of misleading by producing any confusion of individuals, 

 and because it was already in use as the name of many in this family without having been 

 rigidly limited to any one species. I have also chosen the term syenite as the generic term 

 of a set of rocks generally allied to these, and which had already been applied to that 

 rock by Werner, excluding from this denomination the original and classical syenite, w hich , 

 as well in geological connection as in mineral character is a mere modification of granite. 

 The compound term syenitic granite may be applied to this, as I have remarked in a former 

 paper. Varieties intermediate between common trap and syenite may be called syenitic 

 trap. 



