Yol. 50.] ACID KOCKS OF THE INNER HEBRIDES. 229 



whole series. Having demonstrated in the present paper how fully 

 my reading of that locality was justified, I confidently appeal to 

 the vast mass of evidence which is given in my memoir in the 

 Transactions of the Royal Society of Edinburgh, as furnishing a 

 body of proof sufficient to place this question finally among the well- 

 established facts of British Geology. 



EXPLANATION OF PLATES XIII. & XIV. 



Plate XIII. Banded gabbro in the Tertiary volcanic series, ridge north of 

 Druim an Eidhne, Grlen Sligachan, Skye. (From a photograph.) 



The portion of gabbro here represented is an abrupt face of rock about 

 7 feet long by 5 feet high. The darker bands show where the iron ores 

 and ferro-magnesian constituents predominate; the paler layers consist 

 mainly of plagioclase. 



Plate XIV. Dyke of granophyre (6 to 10 feet broad) proceeding from the 

 main mass and intersecting the banded gabbros. (From a photograph.) 



The camera, in taking the original photograph, was placed on the main 

 body of granophyre from which the marginal spherulitic arid dow-structures 

 can be traced up into the dyke. The dark mass to the left of the dyke is a 

 portion of the banded gabbros lying between the dyke and the main mass 

 of granophyre. 



Discussion. 



The President said that he had listened with much interest to 

 the reading of Sir Archibald Geikie's paper ; the Author had made 

 out his case so clearly that no one, it might be supposed, could for 

 a moment doubt that the interpretation which he had given was the 

 correct and the only one ; nevertheless, he had reason to believe that 

 Prof. Judd had, with careful study, arrived at quite a different view 

 of these same rocks. No one could doubt the abilities of these 

 eminent geologists, and he must therefore conclude that the naturo 

 of the country was such as to render agreement very difficult, and 

 the possibility of two observers arriving at quite different views, 

 on the same ground, extremely easy. 



Prof. Judd remarked upon the circumstance that the Author's 

 opening statement, though professing to be historical, entirely 

 ignored the labours of John Macculloch and J. D. Porbes, who, from 

 observations made at the very spot treated of in this paper, were 

 first led to the conclusion that the gabbros of Skye are younger 

 than the granites. 



The speaker entirely agreed with the Author that the gabbro of 

 the Cuillin Hills consists of a great number of sheet-like intrusions, 

 sometimes showing the banded structure so common in the granu- 

 lites. He had, indeed, gone much farther than this, and argued 

 that these sheets are composed of the materials that had consolidated 

 in the great ducts or fissures giving vent to the abundant currents 

 of basaltic lava. He agreed, moreover, with the Author as to the 

 great profusion of veins which traverse both classes of rock, and in 

 his conclusion that these are really ' contemporaneous ' or ' segre- 

 gation-veins.' Nor did he dissent from the view that the granites 

 frequently become fine-grained (' microgranitic ' and * f'elsitic ') in 

 the peripheral portions of their mass. 



