122 Geological Notes from A rraii. [Sess. 



hours or so trying to hit on it. However, I managed to secure 

 a specimen very close to the junction, which shows the slates 

 much altered and mixed with the intrusive granite. 



The granite of this district is of rather a coarse texture, and 

 the mica in it is of the black variety known as " biotite." 

 The granite appears to be very susceptible to weathering- 

 agencies, and it is curious to note how it is breaking up into 

 great sheets and slabs as it were, and the sides of tbe hills of 

 which it is composed appear to be peeling off like the coats of 

 an onion. On account of the facility with which this granite 

 undergoes disintegration, it is difficult to obtain a good clean 

 specimen. After much labour with the hammer and chisel, I 

 did manage to secure a fairly good piece in Glen Eosa. The 

 day I ascended Goat Fell I took my tools, expecting to get a 

 further supply, but was disappointed. All the granite I met 

 with was so rotten that with all the labour I expended I 

 could not find a piece to satisfy my expectations. That this 

 huge mass of granite in the north of Arran is of an intrusive 

 character is established by the fact that the strata among 

 which it occurs has apparently not had its dip altered to any 

 extent. The slates dip away from the granite in some parts 

 and into it in others, showing that the molten granite ate its 

 way into the superincumbent mass and occupied its place. It 

 must, of course, have been solidified very slowly, and at a great 

 depth below the surface, or it would not possess the crystalline 

 character it has. That it now appears considerably above the 

 level of the surrounding rocks is owing to the fact that they 

 are of such a nature as to be more easily eroded. Since the 

 intrusion of the granite an immense mass of overlying strata 

 must have been removed ; and after the exposure of the huge 

 dome-like boss of granite, it has itself been deeply trenched 

 by atmospheric agencies till the district has at length assumed 

 its peculiar rugged aspect. 



A journey across the island from Brodick to Blackwater- 

 foot well repays the geologist in interesting details. There 

 are two so-called coaches which undertake to convey tourists 

 for a moderate charge, but they are so badly horsed that my 

 feelings of consideration towards the poor creatures forbade 

 me to add my modest weight to their burden. The proprietor, 

 I am told, is regularly prosecuted by the Society for the Pre- 



