Mineralogy of Sky. Vl5 



sandstone, and which increase the difficulty of distinguishing be- 

 tween the two substances at that distance from which alone they 

 are visible. Hence it is with some doubt that I must speak of the 

 absolute nature of the whole strata between Portree and Holme j 

 a matter fortunately of no serious moment, as geologists are well 

 aware of the intimate connection subsisting between these strata, 

 which have been fully examined and described in many parts of 

 the British islands. 



Alternations of micaceous shale and of brown sandstone are 

 found in the calcareous beds, of which the colour and composition 

 vary materially, although the predominant colour is smoke-grey, 

 the aspect earthy, and the composition argillaceous. The only 

 organic remains which I could find among them were a large am- 

 monite and a belemnite often exceeding a foot in length. As far 

 as I can discover, our conchologists have not yet ascertained these 

 species or distinguished them by specific names. 



But it is unnecessary to enter into minute details respecting this 

 limestone, since it must be already seen that it belongs to the lias, 

 a rock well known to geologists, and already often described under 

 all its varieties of aspect. 



I shall take some future opportunity of describing this important 

 series as it occurs throughout the western islands, since it is so dis- 

 persed as to involve the history of many of them, and to render it 

 impossible to give an adequate account of it in a paper so local as 

 this. 



Proceeding northwards along this shore, it appears that the beds 

 which follow are superior in position to the preceding. This 

 should result from their general dip, but it cannot be distinctly 

 ascertained. Here, common shale begins to appear in alternation 

 with the other substances, and the quantity of siliceous schistus 



z2 



