ARRAN. GEOLOGY. SCHIST. 361 



ingly no attempt to define it is made. But it is 

 still apparent that the series of argillaceous schist 

 occupies the north-eastern side of the mountains, and 

 that of micaceous schist the south-western ; and that 

 the line of separation between the two, lies in a gouth- 

 eastern direction. If, in examining these two regions, 

 it is observed that they do not invariably adhere to 

 the characters by which the two series are elsewhere 

 distinguished, the causes of this irregularity are not 

 difficult to assign. It is in the first place possible 

 that a part of the north-eastern series, or that of the 

 argillaceous schist, may be found on the south-western 

 shoulder of the mountains ; a circumstance which would 

 naturally arise from the granite having intruded in an 

 irregular manner along the common boundary ; while 

 the same cause may have separated a portion of the 

 south-western series so as to have transferred it to the 

 opposite quarter. It is also to be recollected, with 

 respect to the series of argillaceous schist, that it 

 naturally contains beds of micaceous schist; while here, 

 as in other similar situations, it undergoes various 

 changes of aspect from the influence of the neighbouring 

 granite. 



Such is the separate topography, as far as it appears 

 capable of being ascertained, of the two classes of schist 

 which constitute the schistose tract of Arran. Whatever 

 uncertainty may still exist in this respect, is fully accounted 

 for by the circumstances that have been stated ; while 

 the general facts are proved to be correct, not only 

 by the analogy already mentioned, but by an examination 

 of the different species of schist which constitute each 

 mass. These will be found in every respect identical 

 with those which occur in the two analogous series 

 on the mainland ; subject only to those differences 

 which the preceding statements are fully competent to 

 explain. 



The discordant opinions which have been entertained 



