Mineralogy of Sky. 169 



is found at the foot of the ascent of Ben-na-caillich, so syenite 

 abounds on the opposite side of the valley, while every where 

 throughout it patches of the latter rock, often of very small extent, 

 are found surrounded on all sides by limestone. 



I must further add to the description of the limestone that 

 pectines of considerable size are found among its upper beds, to- 

 gether with terebratulas, and numerous fragments of shells of which 

 some resemble portions of mytili, but the whole in too imperfect a 

 state to admit of accurate examination. 



The description of the limestone of Sligachan having in the 

 original paper been left imperfect, I may now add to it the follow- 

 ing particulars. Beds of the stratified limestone and shale, succeeding 

 a narrow portion of the red sandstone, and precisely resembling 

 the strata of Broadford, extend from the portions of irregular lime- 

 stone before mentioned to the shore of the loch. These also dip 

 to the north-west, but at a considerable angle, and the direction of 

 their elevated edges, like that of all the regular rocks of Sky, is to 

 the north-east, or thereabouts. It is evident that this limestone is 

 a portion of the same series which occupies Strath, the intermediate 

 parts having been either displaced or overwhelmed by the syenite. 



The circumstance of greatest difficulty in comparing these two 

 portions of limestone, is the intervention of the red sandstone, in 

 conformable position, and therefore apparently alternating with 

 them, since the angle of inclination has in all the same tendency. 

 It is not easy to admit of this alternation consistently with what we 

 know of the relative positions of the red sandstone with limestone 

 of this character in other places. Unfortunately Sky itself offers no 

 clue by which we can trace this connection more intimately, or 

 on which we could found some theory of it less at variance with 

 ordinary experience. Whatever the nature of this difficulty may 

 be, I must for the present suffer it to remain unexplained, since 



