LAMLASH. GEOLOGY. 437 



appearances. That portion alone is conspicuous as con- 

 taining the pitchstone vein ; but the accompanying 

 drawing will supersede the necessity of any description 

 of it. * 



With the exception also of one vertical vein of trap, 

 which is seen in the same drawing, it seems unnecessary 

 to notice those which occur in Lamlash, as they are 

 attended with no interesting appearances. That example 

 is remarkable for its spheroidal structure ; a circumstance 

 rarely found in those veins. 



The pitchstone above mentioned, which is also repre- 

 sented in the drawing, is disposed in a manner of which 

 no analogous example has yet occurred throughout this 

 survey, and offers some interesting peculiarities. 



The alternation of rocks found at this place, consists 

 of sandstone, trap, conglomerate, and clinkstone ; the 

 sandstone, which regulates the position of the rest, dipping 

 northwards in an angle of about twenty degrees. The 

 vein of spheroidal trap intersects the whole of these rocks, 

 and is accompanied at no great distance by an upright 

 vein in a parallel direction, which can however be traced 

 only through the mass of horizontal trap. There is much 

 confusion about this place, occasioned by the fragments 

 of conglomerate and the fall of rubbish ; while the form of 

 the cliff, requiring both hands and feet to preserve the 

 spectator's position, renders it impossible to examine the 

 appearances with all the care that could be wished. Some 

 favourable change in the state of the ground may, perhaps, 

 allow of free access hereafter ; but, in the meantime, no 

 error will be occasioned by assuming the latter vein as thus 

 limited, since no conclusions will be drawn from this 

 assumption. It varies from a foot to six inches in breadth. 

 Where widest, the middle portion consists of a fine and 

 compact black basalt, containing occasional particles of 



* Plato XXIV. fiij. 2. 



