RUM. GEOLOGY. 485 



of augit rock, which although it occurs in other parts 

 of Scotland, and is mentioned on several occasions in 

 this work, is no where else so conspicuous and abundant. 

 It varies considerably in aspect, being sometimes of 

 a small granular texture, and scarcely to be distin- 

 guished from common greenstone. Some of these 

 specimens, however granular, break in directions parallel 

 to one or more faces of a large crystal, all the minuter 

 faces of the augit which form the fractured surface, 

 reflecting the light at the same angle. In other places 

 the rock is large grained, the crystals, or grains of 

 each substance being of considerable size, and dis- 

 tinctly aggregated. In this case it often forms a 

 beautiful compound, from the strong contrast of the 

 two minerals ; that beauty being much increased where 

 the felspar is glassy, as it generally is on the highest 

 summits of the two hills Halival and Haiskeval. Some- 

 times the felspar predominates over the augit, at others 

 the rock is a mere mass of crystallized or compact 

 augit. The augit varies in colour, from a dark olive 

 green, to an intense black. Occasionally hornblende 

 enters into the composition, and in certain cases becomes 

 so prevalent that the rock passes into common basalt 

 or into greenstone ; while in others the augit itself is 

 so gradually excluded and the felspar so far increased, 

 that it passes into syenite, or into compact felspar. In 

 a few instances brown mica occurs in the compound. 

 The changes into syenite being the most interesting will 

 be noticed more particularly hereafter. 



Tracing this rock from the place above mentioned, it is 

 found forming the summits of Halival and Haiskeval, as 

 well as many of the lower eminences in the neighbourhood. 

 Its greatest extent is toward the eastern side of the island, 

 where, besides the hills already mentioned, it appears 

 to form the whole of the upper part of Ben more. 

 That opinion is founded on the general aspect of the 

 mountain and on the nature of some detached fragments, 



