J46 NORTH UIST. GEOLOGY. 



by the intervention of micaceous schist, and that it is 

 the third rock in order from granite. It has been shown 

 that in lona, clay slate is in contact with granite, 

 and it will here be seen that it is in contact with 

 gneiss, nay probably, in a state of alternation with 

 that rock. 



If we follow the eastern shore of North Uist. we 

 find the same argillaceous schist occupying the whole 

 line, with trifling exceptions, wherever at least that 

 shore is accessible ; and forming the lowest skirt of 

 the range of hills here denominated the ridge of Heval. 

 As may be expected, it varies considerably in different 

 places, but after what has been already said in describing 

 the small islands in Rueval, it is unnecessary to dwell 

 on these variations. In many parts of this line, gneiss 

 as well as schist is seen ; the two rocks occurring in 

 an irregular manner, and mixed in such a way as to 

 give the greatest reason for supposing that they alternate. 

 But if alternation can only be admitted where beds of 

 one substance are found distinctly interchanged with those 

 of another, it cannot be proved to exist here, on account - 

 of the extreme confusion which attends these rocks. 

 Though the schist and gneiss occur alternately, neither 

 of them is straight even for a small space, so that the 

 relations which the one bears to the other cannot be 

 determined. It is not in the least uncommon to find 

 vertical beds in one place, and not an hundred yards 

 from them others equally regular and absolutely ho- 

 rizontal. 



The next rock that occurs in Heval has an external 

 form and aspect precisely similar to that of the gneiss 

 which it accompanies, being rounded and difficult of 

 decomposition, and causing the hills to appear as if 

 paved with rocks, to the almost total exclusion of ve- 

 getation. The beds, like those of the gneiss, are irre- 

 gularly placed, occupying every possible direction, and 

 being much contorted and dislocated. It alternates, 



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