254 ACCOUNT OF THE MINERALOGY 



This arrangement of the mass of beds, prevails with great 

 uniformity throughout; we observed them to deviate only in one 

 instance from it, at the western extremity of Myggenaes, where 

 they rise abruptly to an angle exceeding 45°. There was no 

 particular uniformity that we perceived, in the succession of 

 the different kinds of trap, although such might perhaps be dis- 

 covered on more minute investigation. The trap-tuff was more 

 abundant than any of the other varieties, and was often the 

 only material we could distinguish, in cliffs of tremendous 

 elevation, in which we sometimes found it difficult to trace 

 the separation of the different beds. When greenstone or 

 amygdaloid are interposed, the separations are better defined, 

 and are often divided, by a layer of brick-coloured fine- 

 grained tuff, which passes into the substance of the adjoining 

 bed, and is analogous to the red material which forms so stri- 

 king a feature in the basaltic promontories of the Giant's 

 Causeway. The grandest display of greenstone which we met 

 with was at Zellatrae in Osteroe, where the bed, like that 

 of Fairhead, is three hundred feet thick, and split in a similar 

 manner, into prismatic concretions, which, at a distance, give 

 it a regular columnar appearance. On the top of the hill, at 

 Leynum, I found the greenstone in the rude columnar form, 

 which it assumes on the south-west side of Arthur's Seat; 

 and in Nalsoe, as well as in some other of the islands, we no- 

 ticed ,beds of a description quite new to me. Being considera- 

 bly elevated in the cliff, we could not ascertain the dimensions 

 with accuracy. I think, however, that, in Nalsoe, may be 

 from forty to 'fifty feet thick ; it is composed of vertical co- 

 lumns, enormously thick. In some the diameters were little 

 short of their length ; and although they stand straight upon 

 the base, they are all bent at the sides, so as to present an ir- 

 regularly waved line between each. The most singular cir- 

 cumstance 



