144 NORTH U1ST. GEOLOGY. 



as much by their external aspect as by their structure, 

 and ought to be ranked as portions of North Uist. 

 There is also a chain of small islands lying off the 

 mouth of Kyleswia, which, although more apparently 

 connected with Benbecula, appertain in geological cha- 

 racter to the islands in Rueval, now to be described. 

 As I did not examine all the small islands scattered 

 along this shore, some, which I have judged to belong 

 to the gneiss of Benbecula, may perhaps prove, like 

 Rona, to be parts of the rock of Heval : but these 

 omissions are of no importance. 



Close to the two Flotas is a small island, not named 

 in maps, which is here selected on account of its 

 simplicity, as a foundation for the description of these 

 obscure rocks. It consists of an argillaceous schistus 

 of a pale grey colour, placed in beds nearly horizontal 

 or with a small elevation, and apparently with very 

 little disturbance. Some of the small rocks and islands 

 in the neighbourhood exhibit a similar construction 

 with slight variations. The schist is sometimes of a 

 dark lead blue, of a more compact texture, and less 

 regular in position ; and in many places it contains 

 green compact felspar diffused through it in threads 

 and laminae. In some other places it assumes a diversity 

 of character; and among these, Flota beg and Flota 

 more offer the largest surfaces for examination. The 

 schist is in these islands occasionally traversed by 

 granite veins, similar in aspect and composition to those 

 which traverse the gneiss of the neighbouring parts. 

 This may be adduced as a proof of the posteriority 

 of these veins to the rocks which they intersect; 

 since they are here, as in Coll, found to pass indis- 

 criminately through two different rocks, of which the 

 one appears from its position to be of more recent 

 formation than the other. It was already remarked 

 in describing lona, that where the argillaceous schist 

 approaches to the mass of granite it acquires a new 



