436 Professor K. Busz — Granophyre Dyke in Scotland. 



II, — On a Granophyke Dtkk intrusive in the Gabbro of 

 Aednamueohan, Scotland. 



By Professor K. Busz, Ph.D., of Miinster. 



LAST year, while on an excursion to Scotland, I visited the 

 Ardnamurchan peninsula, which, as is well known, consists to 

 a great extent of rocks belonging to the gabbro family. On the road 

 leading from the little village of Kilhoan, opposite the Isle of Mull, 

 on the north coast, a small quarry has been opened for road-metal, 

 which shows an exquisite section of a granophyre dyke intrusive in 

 a dark and almost black fine-grained rock, which the microscopic 

 examination proved to be a gabbro. This is, therefore, a similar 

 occurrence to that of Barnavave, Carlingford, Ireland, which has been 

 admirably described by Professor Sollas, and also that of Strath 

 in the Isle of Skye, of which Mr. Harker has given us a detailed 

 account. As occurrences of this kind seem to be rather rare and, as 

 far as I am aware, hitherto not known from Ardnamurchan, I may be 

 excused for calling your attention to the following short description 

 of these rocks, although there is but little to be added to the results 

 attained by the skilful researches of the above-mentioned authors, 

 and it only shows again that on Ardnamurchan we are to expect 

 very nearly the same geological phenomena as in the adjacent 

 islands, in particular in Skye and Eum. 



I will now describe, firstly, the gabbro and try to explain its 

 alterations due to the intrusion of the granophyre dyke, and 

 secondly, the granophyre, and the effect which the gabbro, through 

 having been partly absorbed, had upon its composition. 



1. Gabhro. The rock under consideration is, as far as I can 

 judge, a dyke-rock, and is exactly like some of the dykes which 

 occur in connection with the large gabbro masses of the Odenwald 

 Mountains in Germany, which have been carefully examined and 

 described by Professor Chelius, of Darmstadt. Owing to the very 

 unfavourable weather and the fact of the whole neighbourhood 

 being covered by deep moorland, I was unable to trace the extension 

 of the dyke, and can therefore now only give an account as to how 

 it is exposed in the quarry. The centre of the latter shows the 

 dyke to a width of about two yards, and it is then covered on both 

 sides by debris, so that the entire thickness is certainly greater. 

 The composition and structure of the rock is not the same in all 

 its parts. 



The main mass consists of a rock almost black and of a fine 

 sugar-grained structure, similar to some dense quartzites, and 

 contains no microscopically visible excretions. By the aid of a lens, 

 however, the rook is seen to consist of small grains of a grey and 

 black colour. 



The structure as exhibited in the microscope is exquisitely panidio- 

 morphic, according to Rosenbusch's nomenclature, the essential 

 constituents being felspar and pyroxene, both in grains of about 

 equal size. Both in structure and composition it coincides exactly 

 with those dyke-rocks of the Odenwald district which Chelius named 



