438 LAM LASH. GEOLOGY. 



analcime, mesotype, and glassy felspar. On each side there 

 is a lamina consisting of a black substance intermediate 

 between basalt and pitchstone ; gradually passing into 

 perfect pitchstone at the surface where it is in con- 

 tact with the trap. In this part it is of an intense 

 black colour and vitreous aspect, but forms a mere 

 crust, scarcely amounting to one-tenth of an inch 

 in thickness. There is in this case an obvious line of 

 separation between the outer laminae on each side and the 

 central basalt. In the thinner parts of the vein, there 

 appears to be no central basalt, a regular transition taking 

 place from each side to the middle ; the former being of 

 perfect black pitchstone, and the whole interior consisting 

 of the intermediate substance just mentioned. The re- 

 semblance between these parts of the vein and the pitch- 

 stone of Egg is very strong ; and in that, it will be remem- 

 bered, the black pitchstone is found only at the sides 

 of the vein ; the central parts, wherever it is sufficiently 

 wide, presenting an intermediate substance, differing, it is 

 true, in colour from this, but resembling it in every other 

 particular. 



Whatever conjectures may be formed respecting the 

 cause of this singular appearance, it is as yet too insulated 

 to afford legitimate grounds for any conclusion. The 

 passage of basaltic veins through basalt or other trap 

 rocks, is by no means uncommon ; and numerous instances 

 can be pointed out through the whole of the trap districts 

 of Scotland, unattended by any indications of a similar 

 change. Hereafter, when a greater number of facts shall 

 have been collected towards the history of pitchstone, this 

 example may acquire additional value. 



It was already noticed in treating of Arran, that blocks 

 of the granite of Goatfell are found scattered over the 

 shores of Lamlash : but I need add nothing: to the remarks 



' O 



then made on the migration of these blocks. 



I may conclude the history of this island by mentioning 



