212 SIR ARCHIBALD GEIKIE ON THE BASIC AND [May 1 894, 



16. On the Relations of the Basic and Acid Rocks of the Tertiary. 



Volcanic Series of the Inner Hebrides. By Sir Archibald 



Geikie, D.Sc, LL.D., F.R.S., F.G.S. (Read February 21st, 



1894.) 



[Plates XIII. & XIV.] 



Contents. 



Page 



I. Introduction 212 



II. The Gabbro Bosses 216 



III. The Granophyre Bosses 218 



IV. Conclusion 227 



I. Introduction. 



Before entering upon the special subject of the present paper, I 

 wish to be permitted to make certain personal explanations which 

 appear to me to be necessary on this occasion. Having in my 

 early years had the good fortune to spend much time among the 

 Western Islands of Scotland, I was soon fascinated by the geological 

 features of that picturesque region. Like most young geologists, I 

 began with the fossils and collected largely from the Jurassic 

 formations of Skye and the adjacent islands, though the interesting 

 problems presented by the general structure of the area, and more 

 particularly by the igneous rocks, could not wholly escape the 

 attention of an enthusiastic beginner. The results of these youthful 

 labours were eventually communicated to this Society in the year 

 1857. 1 



Having been appointed to the Geological Survey in 1855, I had 

 the inestimable advantage of a practical training in methods of 

 detailed geological mapping, and it so happened that this training 

 lay, in large measure, among the ancient volcanic rocks so copiously 

 developed among the Old Red Sandstone and Carboniferous forma- 

 tions of Central Scotland. I was thus led from the very outset to 

 take a keen interest in volcanic geology, and the experience gained 

 among the records of Palaeozoic eruptions induced me to return to 

 the study of the latest series of volcanic outbursts in Britain — those 

 of the Western Isles. From time to time I communicated to the 

 Royal Society of Edinburgh accounts of my investigations. 2 At 

 last, in the year 1871, I had advanced far enough to be able to 

 present to the Geological Society a general outline of the Tertiary 

 volcanic history of Britain. 3 I therein endeavoured to show how 

 extensive in area, varied in petrographical character, and protracted 

 in geological time were the Tertiary eruptions within the area of 

 our islands. This paper was intended to be the first of a series, 



1 Quart. Journ. GeoL Soc. vol. xiv. p. 1, 'On the Geology of Strath, Skye.' 



2 See in particular Trans. Roy. Soc. Bdin. vol. xxii. (1861) p. 649; Proc. 

 Roy. Soc. Edin. vol. vi. (1867) p. 71 ; also Brit. Assoc. Rep. 1867, Sections, p. 49. 



3 Quart. Journ. Geol. Soc. vol. xxvii. p. 279, ' On the Tertiary Volcanic Rocks 

 of the British Islands. — First Paper.' 



