Vol. 50.] ACID ROCKS OF THE INNEK HEBRIDES. 213 



but as I could only snatch a few brief weeks of annual holiday for 

 this extra-official work, my progress could not be rapid. Before I 

 was able to offer to the Society my second communication, Prof. 

 Judd, at the beginning of 1874, read before the Society a memoir 

 ' On the Ancient Yolcanoes of the Highlands.' l As he had been 

 so fortunate as to be enabled to devote many months of continuous 

 labour to the investigation of the region, he succeeded in covering 

 the ground which I meant to occupy. In the belief that in a large 

 part of my own undertaking I had thus been forestalled, I laid aside 

 the design of continuing the series of papers already begun in our 

 Journal. 



Prof. Judd's paper was undoubtedly a bold and brilliant 

 piece of work. Though he had had no previous experience of 

 igneous rocks, he gathered together a large series of observations 

 and generalized from them so ingeniously and suggestively that his- 

 memoir attracted a large amount of notice. And yet, from my own 

 experience in these Western Isles, I knew that there were many 

 difficulties which he had not explained. It was not, however, until 

 the year 1879 that, in the course of a journey through some of the 

 volcanic tracts of Western America, I began to see, as I believed, 

 the meaning of some of the phenomena which had for so many years 

 puzzled me in the West of Scotland. My old love of the subject 

 and of the scenery of the Inner Hebrides was re-kindled, and then, 

 in these wilds of the Par West, I determined to take up once more 

 the study of the history of our Tertiary Volcanoes. At such intervals 

 of leisure as could be seized in the midst of a busy official life, I 

 worked at the subject and, after nine years, was enabled to complete 

 my task. 



So long a period of time had elapsed — no less than seventeen 

 years- — since the publication of my paper on Tertiary Volcanic 

 Pocks in our Quarterly Journal, that it was obviously undesirable 

 to attempt to resume the series of which that paper was intended 

 to be the first. I therefore turned to the Poyal Society of Edin- 

 burgh, which had published my earliest writings on the subject, and 

 offered to it a somewhat voluminous monograph. The Council of 

 that Society accepted my communication, and published it in its 

 ' Transactions ' during the autumn of 1888. 2 



In retracing my former footsteps among the Inner Hebrides and 

 in traversing fresh ground, I was led to form conclusions very 

 different from some of those which had been arrived at by Prof. 

 Judd. It is not necessary for my present purpose to enumerate 

 these differences of opinion ; I will allude to one only, perhaps the 

 most important of all, inasmuch as it affects the whole order of 

 interpretation of the volcanic history. Prof. Judd, as I found 

 from copious evidence collected all over the region, had mistaken 

 the true sequence in the protrusion of the volcanic masses of the 

 Inner Hebrides, putting the great bosses of acid rocks at the begin- 

 ning instead of at the end of the series. It would have been to me 



1 Quart. Journ. Geol. Soe. vol. xxx. p. 220. 



2 Trans. Roy. Soc. Edin. vol. xxxv. pp. 21-184. 



