M U LL. M J N Ell A I,S'. 



ring in Sky, as well as those hereafter mentioned in 

 Arran, are sufficient to prove that this syenite is only a 

 portion of the trap formation, geologically considered ; 

 being connected with it in position, simultaneously 

 formed, and bearing with it a common relation to the 

 surrounding rocks. Nor is the mineral composition of 

 the two separated by a decided line, the change being 

 effected in a manner similar to that which occurs between 

 the augit rock and the syenite of Rum. 



Such are the rocks which, as far as my observations 

 extended, compose the island of Mull. But I must not 

 terminate this account without mentioning the frequency 

 of trap veins throughout the island. These are indeed 

 so invariably present in all parts of Scotland where trap 

 predominates, that I have rarely thought it necessary to 

 give a particular description of them, unless where they 

 were attended with unusual or instructive appearances. 

 I know of few such in Mull. They are frequently con- 

 spicuous for their permanence after the surrounding strata 

 have been removed, a character which they also possess 

 in Isla, .in Jura and elsewhere. One of them has been 

 described in high colouring by Faujas de St. Fond, but 

 there are innumerable others far more conspicuous in 

 the northern division of the island.* 



IN reviewing some of the amygdaloids collected in 

 Mull, I discovered a non-descript substance intermixed 

 with some prehnite, but too small in quantity for exa- 

 mination. Having since found the same mineral in 

 greater abundance in Glen Farg, I shall give the best 

 description of it I am enabled to do from those spe- 

 cimens, as I cannot now assign the exact locality of 

 the former. It has hitherto escaped the observation of 



* I must add to this account of the rocks of Mull, that loose frag- 

 ments of pitchstone have been found by Mr. Greenough upon the 

 southern shore. 



