J48 NORTH UIST. GEOLOGY. 



the venous distribution so generally to be traced in 

 the latter substance rather seems to point it out as 

 a gneiss altered by the subsequent intrusion of this 

 mineral, and thus analogous to the rock described in 

 Barra.* 



The gneiss found on the shores of Loch Maddy, 

 occurs in all the variety of form and composition so 

 often described, and may be traced throughout the greater 

 part of the island. If there is any difference, it consists 

 in the proportion of the straight being greater here 

 to the contorted and displaced rock than in the pre- 

 ceding islands. In some few places I observed beds 

 so thin as to be capable of splitting into leaves not 

 ill suited for heavy tiling, and, in others, it seems to 

 pass, as in similar situations, into an unfoliated syenitic 

 granite. 



The ramified basaltic veins formerly described as so 

 abundant in Barra, are more rare in North Uist; but 

 they also occur, being found in one or two places travers- 

 ing the anomalous rock of Heval, and adding materially 

 to the already complicated nature and obscure appearance 

 of that rock. 



The other trap rocks that occur in this island have an 

 unusual claim on a separate notice, as they present features 

 of rather more importance than in those already described. 



The entrance to Loch Maddy, (the Lake of Dogs) is 

 marked to mariners by two remarkable .detached rocks 

 situated about a quarter of a mile from the shore, named 

 Maddy more and Maddy grisioch. The former is about 

 100 Feet in height, and presents towards the land, a face 

 irregularly columnar and inclined to the perpendicular 

 in an angle of about 20. The latter is much less 

 distinctly marked by the tendency to vertical division, 



* I have since found a similar rock occupying a large tract on 

 the north western coast of Ross-shire and passing into gneiss of the 

 more ordinary characters. It may therefore be safety ranked among 

 the varieties of that rock. 1818. 



