ARRAN. GEOLOGY. SECONDARY STRATA. 375 



colour, common shale, arenaceo-micaceous shale, and 

 bituminous shale, either simple, or containing vegetable 

 remains and impressions. These organic substances, from 

 their length and occasionally parallel outline, resemble 

 the leaves and the compressed stems of reeds. Wherever 

 they occur, their substance is always found on fracture 

 to be composed of an extremely brilliant coal. The coal 

 itself, in the larger masses, is also splendent throughout, 

 containing little bitumen, and burning with difficulty unless 

 it be in a considerable body and strongly heated. 



Independently of these beds of regularly stratified sub- 

 stances, there are to be seen, and particularly near Lagg, 

 great masses of trap conglomerate, but whether forming 

 regular beds or not, it is difficult to determine. There 

 are also many masses of common porphyritic greenstone, 

 and of fine grained greenstone, or of basalt. Some of 

 these are evidently veins traversing the strata, while 

 others, which must also be veins conformable to them, 

 have the appearance of beds. 



The collective thickness of the whole of the series now de- 

 scribed, must be enormously great, as it occupies a space of 

 about two miles on the shore. If the angles of inclination 

 were sufficiently constant, a ready estimate of that thick- 

 ness might be made by computing that side of a right 

 angled triangle which is parallel to the vertical fractures 

 of the strata, the horizontal distance and inclination 

 admitting of measurement. In the actual state of things, 

 only a vague conjecture could be formed. Infinite pa- 

 tience might perhaps succeed in producing a nearer 

 determination by measuring the breadth of each bed ; 

 a toil which would not be compensated by the results. 



Where these beds cease, they are succeeded by red 

 sandstone, forming a mountain mass not less thick than 

 that which lies below them, and reaching beyond the Cock, 

 where it at length terminates. It is here termed sand- 

 stone, as the lowermost mass was called a conglomerate ; 

 merely because the fine sandstone is nearly as predo- 



