Mineralogy of Sky. 159 



The most leading error is that which states the promontory of 

 Sleat as composed of micaceous schistus. This substance occurs 

 in several places, and often in distinct beds of considerable thickness, 

 while in others it consists of mere laminse interposed among the 

 other rocks. These rocks are of very various composition, but as 

 gneiss occurs in considerable quantity among them, exceeding 

 greatly the space occupied by the micaceous schist, the latter will 

 probably be considered by most geologists as subordinate to the 

 former, and the gneiss as being the lowest and fundamental rock 

 of Sky. But the truth is, that this series is not amenable to any- 

 systematic rules, and it will be better to state the fact as it exists, 

 than to incur the risk of a similar error by transferring to gneiss 

 that rank which I had before conferred on micaceous schist. It 

 will be seen that the series presents anomalies which cannot be 

 removed by any theory of subordination, and that the history of 

 the district of Sleat is not the least interesting part of the unex- 

 pected appearances presented by this very instructive island. 



The characters of the gneiss are so strongly marked in one part 

 of the space which it occupies, that there can be no difference of 

 opinion respecting it. Besides mica or hornblende it contains a 

 conspicuous proportion of high red felspar and quartz, being at the 

 same time distinctly laminated, and from the contrast of its colours, 

 very remarkable. 



From this regularity of structure and composition it passes into 

 a substance for which there is no name in the present nomenclature 

 of rocks, and which can only be ranked with gneiss by assuming a 

 considerable latitude of character. This rock is a compound of 

 felspar and quartz with chlorite schist, these substances being still 

 interlaminated as before, so that each mineral generally occupies a 

 distinct portion of the specimen, the latter becoming substituted 



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