436 LAMLASH. GEOLOGY. 



the sandstone strata, and equally appertaining to the class 

 of venous formations. 



The principal of these masses are found towards the 

 south-eastern end of the island ; and, if a cursory view 

 only, be taken of their connexion with the sandstone, 

 it would be concluded, as it has been by some observers, 

 that the trap was inferior to the strata and the felspar rock 

 superior ; the whole forming a regular series. There 

 appears, indeed, at first sight, to be a regular alternate 

 stratification of the white sandstone with the trap, the 

 latter rock being the lowest. This alternation is frequent, 

 and the thickness of the different beds, although variable, 

 is seldom considerable. But if the details be carefully 

 examined, there will be no difficulty in perceiving that the 

 trap is intermingled with the sandstone in irregular por- 

 tions, and not in continuous and parallel beds. In one 

 place it may be observed to terminate suddenly, while, in 

 another, the sandstone is cut through by the meeting of 

 two neighbouring masses of the trap. It must therefore 

 be considered as offering examples of those horizontal 

 veins which have been already sufficiently described on 

 various occasions. In composition, this rock is identical 

 with that occurring in Arran, near Clachland point and 

 elsewhere ; containing augit, felspar, and mesotype : if 

 there are any variations, they seem to consist in the greater 

 or less distinctness of the component parts, and do not 

 require any particular detail. It is proper to add, that 

 here, as in similar situations, the sandstone is much in- 

 durated near its contact with the trap. This is particularly 

 the case with a large portion of conglomerate that occurs 

 in the neighbourhood of the pitchstone about to be 

 described. 



Besides those just mentioned, other masses of trap 

 occur in similar positions towards the southern extre- 

 mity of the island ; but these, with one exception, are not 

 attended, as far as I could perceive, by any remarkable 



