OF THE WESTERIS^ ISLES OF SCOTLAND. 357 



similar rocks which occur in the Faroe Isles, in Iceland, and in 

 Greenland, — districts in which the volcanic products present such 

 remarkable analogies with those of the Western Isles of Scotland. 

 The results of some of these researches have afforded me invaluable 

 aid, for they deal with materials some of which are almost abso- 

 lutely unaltered, belonging to the same types as those which we 

 find in such an altered condition in our own country. 



In 1874 K. Yrba described some rocks from Southern Greenland, 

 and among them certain diorites of somewhat remarkable character, 

 which may not improbably be of the same geological age with rocks 

 to be referred to in the present paper*. 



In 1882, P. Schirlitz published the result of his studies, in the 

 Petrographical Laboratory of Leipzig, of the Icelandic rocks collected 

 by Professor Zirkel in 1860. In addition to the basalts and rhj'o- 

 lites, a number of very interesting rocks, called by Zirkel augite- 

 andesites, was described by this author. He rightly insists, how- 

 ever, on the distinction between these and the Santorin lavas and 

 the glassy andesites of Java (the vitrophyric augite-andesites of 

 Rosenbusch), and is in favour of grouping them with the basalts f. 



In 1884, Dr. A. Osann undertook an examination of the series of 

 specimens from the Faroe Islands contained in the collection of the 

 University of Heidelberg. He showed that, besides the black 

 lustrous olivine-basalts, there exist dark grey rocks of very different 

 aspect, containing an augite of a somewhat remarkable character, 

 and he is disposed to place these among the andesites J. The 

 distinction of these dark grey rocks, poor in olivine, which Osann 

 pointed out in the case of the Faroe Isles, and Schirlitz in the case 

 of those of Iceland, was also made by H. Reusch in the case of the 

 Jan-May en rocks §, and by Nauchoff in the case of the Greenland 

 lavas Ij. 



Last, and most important of all, must be mentioned the very valu- 

 able researches made upon the rocks of Iceland and the Faroe Islands 

 by M. Ilene Breonlf. These researches were carried on in the Labo- 

 ratory of Prof. Fouque in the College de France. M. Breon has 

 described a number of lavas of intermediate composition which pre- 

 sent the most striking analogies with some of the rocks now found in 

 such an altered condition in the Hebrides. The wonderful freshness 

 of the Icelandic rocks enables us to explain many points of diffi- 

 culty which confront us in the case of their greatly altered British 

 representatives, and I am much indebted to M. Breon for his kind- 

 ness in sending me a series of specimens of his Icelandic types for 

 comparison w^ith the rocks of Scotland. 



* Sitzuugsb. Wien. Alcad. Ixix. (1874\ pp. 100-115. 



t Tschr. Mill, und Petrogr. Mittheil. iv. (1812), p. 414. 



+ Neues Jabrb. fiir Min. &c. 1884, i. pp. 4o-49. 



§ 'Tbe Norwegian North-Atlantic Expedition of 1 870-78 ' (Cbristiania, 

 1882). 



II Min. Mittheil. 1874, pp. 100-170. 



•[ Notes pour servir a I'ttude de la Geologic tie I'lslande et des lies Fccroe 

 par E. Eivon, 1884. 



a. J. G. S. No. 183. 2 D 



