LUIXG. GEOLOGY. 



copper coloured mica; being almost identical in composition 

 with a rock formerly described in Kerrera. That which 

 renders it peculiarly interesting, is the general parallelism 

 of the mica; a circumstance which does not occur to 

 the same degree in that rock, which, it will be re- 

 membered, is a rudely columnar and overlying mass. 

 As this is an unstratified substance, and as there can be 

 no question respecting its intrusion in the form of a 

 vein, the mica must have been crystallized in the mass, 

 and its parallel disposition is therefore the result of 

 that polar tendency among distinct crystals which I 

 have formerly noticed in speaking of the graphic granite 

 in Coll. It will immediately be seen how this circum- 

 stance bears on the question of micaceous schist, as 

 well as on that of gneiss ; since in those cases the 

 laminar disposition of the mica may equally be attributed 

 to this crystalline polarity. I shall pursue the subject 

 no further ; it is one of the many obscurities remaining 

 to add interest to pursuits which would soon lose all 

 their attractions if there was nothing left for future 

 inquiry.* 



In concluding this account of Luing I have to add 

 one remark, which applies not only to the schistose 

 islands already enumerated, but to many of those about 

 to follow. This is the absence of alluvial deposits or 

 transported materials. There are no rivers capable of 

 producing recent accumulations, and, as far as I have 



* This being however an interesting question, as it relates to the 

 rocks last named, it will not be amiss to add some other facts of an 

 analogous nature which bear on it. 



The pinite of Ben Gloe, described in the Geol. Trans, is generally 

 found in prisms so short as to be mere scales. These invariably maintain 

 a parallel position. The same circumstance is extremely common in the 

 mica, which occurs, like this mineral, in veins of porphyry. In one 

 of the varieties of the hypersthene rock of Sky, the crystals of that 

 mineral arc laminar, and placed in a position similarly parallel to each 

 other, and, as in gneiss, to the plane of the bed in which they lie; 

 although this rock is unquestionably an unstratified substance. 



