DURING THE TERTIARY PERIOD IN THE BRITISH ISLES. 125 



tion, and to the stormy climate, — a formidable list of barriers, in presence of which 

 he leaves the relative position and age of the rocks unsettled.* 



Von Oyenhausen and Von Dechen, who wrote so excellent an account of their visit 

 to Skye, and who traced much of the boundary-line between the gabbros and the other 

 massive eruptive rocks (syenite), seem to have made no attempt to work out the 

 connection between the former and the rest of the volcanic rocks, t 



Principal Forbes, in his able sketch of the Topography and Geology of the 

 Cuchullin Hills, appears to have been the first to recognise the superposition of the 

 " hypersthene rock " upon the "common trap rocks " — that is, the plateau-basalts. He 

 was disposed to consider the " hypersthene mass as a vast bed, thinning out both ways, 

 and inclined at a moderate angle towards the S.E."| 



Professor Judd regarded the bosses of basic and acid rocks that rise out of the bedded 

 basalts as the basal cores of enormously denuded volcanic cones. He believed the 

 granitoid rocks to have been first erupted, and that after a long interval the basic masses 

 were forced through them, partly consolidating underneath and partly appearing at the 

 surface as the plateau-basalts. § That the order of appearance of the several rocks 

 has been exactly the reverse of this supposed sequence will, I think, be fully established 

 in the present memoir. Professor Zirkel recognised that the gabbros are a dependence 

 of the basalts, that they overlie them, and that on the naked flanks of the mountains 

 they are regularly bedded with them. || 



So far as I can learn, however, no one has yet traced out in more detail the actual 

 boundaries of the several rocks on the ground, so as to obtain evidence of their true 

 relations to each other as regards structure and age. Some of the numerous impedi- 

 ments recorded by Macculloch have no doubt retarded the investigation. But, as 

 Forbes so well pointed out, there is really no serious difficulty in determining the true 

 structural connection of the amorphous rocks with each other and with the bedded 

 basalts of the plateaux. I have ascertained them in each of the districts,! and as the 

 result of my examination I may briefly state here that there cannot be the least doubt 



* See his Western Islands, vol. i. pp. 368, 374, 385, 386. With much admiration for the insight and zeal, amount- 

 ing almost to genius, which Macculloch displayed in his work among the Western Islands, at a time when, with poor 

 maps and inadequate means of locomotion, geological surveying was a more difficult task than it is now, I have found it 

 impossible to follow in his footsteps with his descriptions in hand, and not to wish that for his own fame he had been 

 content to claim credit only for what he had seen. His actual achievements were enough to make the reputation of 

 half-a-dozen good geologists. It was unfortunate that he did not realise how inexhaustible nature is, how impossible 

 it is for one man to see and understand every fact even in the little corner of nature which he may claim to have 

 explored. He seems to have had a morbid fear lest any one should afterwards discover something he had missed; he 

 writes as if with the object of dissuading men from travelling over his ground, and he indeed tacitly lays claim to any 

 thing they may ascertain by averring that those who may follow him " will find a great deal that is not here described, 

 although little that has not been examined " (p. 373). Principal Forbes long ago exposed this weak side of Maccul- 

 loch and his work {Edin. New Phil. Jour., xl. (1846) p. 82). 



t Karsten's Archiv, i. p. 99. They frankly admit that " the relation of the hypersthene-rock to the other trap 

 rocks was not ascertained." j Edin. New Phil. Jour., xl. (1846) pp. 85, 86. 



§ Quart. Jour. Geol. Soc, xxx. (1874) p. 249. || Zeitschrift. Deutsch. Geol. Gesellsck, xxiii. (1871) pp. 58, 92. 



II In two of my excursions in Mull, and once in Skye, I was accompanied by my colleague Mr H. M. Cadell, and 

 I gladly acknowledge the great assistance he rendered me in mapping those regions. 



VOL. XXXV. PART 2. v 



