78 Dr. Mac Culloch's Sketch of the 



situations. They are to be observed pretty frequently passing through 

 the reck at Coruisk, and through the greenstone and cHnkstone of 

 Garsven, in the neighbourhood of which latter they abound. Their 

 compactness and lustre are frequently so great that they approach in 

 appearance to that pitchstone which forms the basis of the beautiful 

 columnar porphyry of Egg. In addition to this feature they are 

 strongly distinguished from the trap veins that traverse the sand- 

 stone by the intimate and almost inseparable union which they form 

 with the body of the rocks which they traverse, whereas the latter 

 are separated with the greatest ease. 



There is still another set of veins found in this place, which how- 

 ever even and compact they may appear on a fresh fracture, and thus 

 resembling basalt, appear to consist of clinkstone. This may be con- 

 cluded from the facility with which they decompose at the surface 

 into a greyish or whitish earthy looking substance, and from the 

 depth of that decomposition. They are further distinguished by the 

 frequency and minuteness of their ramifications, which are often 

 drawn out to the size of a thread. Veins of this description have not 

 as far as I know, been noticed, but they are not uncommon in the 

 western islands, and they abound particularly in some parts of the 

 Long isle ; in this place they are chiefly seen on the borders of 

 the small and picturesque lake Coruisk, and are found traversing the 

 hypersthene rock, as well as the veins themselves, which consist of 

 this mineral. 



Hiving now described the trap veins which pass through the 

 mountain trap, and those, perhaps more important ones as far as re- 

 lates to that rock, which do not pass through it, I must turn the 

 reader's attention to those which are found in the stratified trap. 

 These are not very abundant, but may be seen distinctly among 

 ether places on the western shore, traversing the lofty cliffs in various 



