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, together with terebratulæ, 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 following 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 limestone 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
