67 



slate as above described, there occur two distinct varieties of the 

 rock a coarse and a fine grained, not intermingled with one another, 

 but occupying separate portions of the district. Mr. Ramsay called 

 attention to these marked varieties, and traced approximately the 

 limits of each. We have somewhat extended the bounds of the fine 

 grained variety. It occupies the space between the Ben-Varen and 

 Cior-Mhor ranges, rising high up on the east front of the former, and 

 on the west front of the latter reaching as far up as the passes from 

 Glen lorsa into Glen Rosa and Glen Sannox. It crosses the water- 

 shed at Loch-an-Deavie, and stretches from half a mile to a mile 

 north-east toward the base of the Castles, and down also into Glen 

 Eais-na-Vearraid. The coarse variety covers the rest of the district, 

 and forms the tops of all the mountains. The Goat fell group is 

 composed entirely of it ; as are also the whole east front and all the 

 summits of the Cior-Mhor range from Ben-Ghnuis to Suithi-Fergus ; 

 along the back of the range the fine grained variety reaches the 

 heights already noticed. Extending hence across the valley of the 

 lorsa, it rises on Ben-Yaren as high as the base of the last steep 

 ascent. The rest of the range is of the coarse variety. The two 

 kinds are very distinct from one another, though the component 

 minerals are the same. Both consist of quartz, felspar, and mica, 

 the two first being in nearly equal proportions, the last in less quan- 

 tity than either. In neither kind is this mica replaced by horn- 

 blende, so as to form the variety called syenite. This rock is indeed 

 found in Arran, but not within the district called the granite nucleus. 

 There are, however, several varieties of both kinds ; but these are 

 merely dependent upon slight changes in the colour or size of the 

 constituent crystalline grains. The fine variety of the interior has 

 often an arenaceous aspect and sandy feel, from the minuteness of 

 the grains. The distinctness of these two varieties of granite in 

 their mineral aspect, and the fact that they do not intermingle, but 

 occupy separate tracts, led Mr. Ramsay to conclude that they were 

 of different ages, and that this fine grained variety was the newest 

 rock in the whole island. He rests this conclusion on the non-exis- 

 tence of whin dikes in the fine granite, and on what he seems to state 

 with the confidence of personal observation, namely, that " in cut- 

 ting through the coarse granite, these dikes frequently approach the 

 borders where it joins the fine variety, and are then invariably cut 

 sharply off by the fine granite, when they approach it in the coarser 

 kind," (p. 65). We have never noticed any instance in which a 

 dike is thus cut sharply off, nor does Mr. Ramsay refer to any spot 

 where such a case occurs, and it is possible he may refer merely to 



