242 MESSES, PEACH, GUNlsT, AND NEWTON ON [May I9OI, 



llaasay and Skye, but had found no recognizable Rhgetic species ; 

 and although Mr. Macconochie and Mr. Tait had since met with much 

 better specimens in Skye, no distinctive E-hastic species could witli 

 certainty be identified. It was therefore highly satisfactory that 

 characteristic fossils from this formation had now been discovered 

 in Arran, in beds which, judging from their extent, could not be far 

 removed from the parent source. 



Mr. G. W. Lamplugh inquired whether, besides the blocks that 

 had fallen into the vent from higher levels, there were any sedi- 

 mentary masses raised from lower horizons by the volcanic forces. 



The Rev. J. F. Blake and Prof. W. W. Watts also spoke. 



Sir Archibald Geikie replied, on behalf of the Authors of the 

 paper, to some of the questions- raised' in the discussion. He 

 remarked that there were two points of more especial interest 

 in the discovery which had that evening been announced to the 

 Society — the proof supplied as to the age of the youngest eruptive 

 rocks of Arran, and the evidence furnished of the stupendous 

 denudation of the country since the time of the Chalk. With 

 regard to the first of these points, it would be remembered that early 

 in the last century Macculloch had shown that, as no fragments of 

 the Arran granite were to be found in the surrounding E'ed Sand- 

 stones, that rock was presumably younger than these strata. As 

 far back as 1873 the speaker, after a prolonged study of the igneous 

 masses of Skye and Mull, had expressed the opinion that the Arran 

 granite would probably be found to belong to the great Tertiary 

 Tolcanic Series of the North of Ireland and West of Scotland. The 

 recent observations of Messrs. Peach & Gunn, and the confirmatory 

 determinations by Mr. Newton, put the matter beyond all further 

 dispute. The Hed Sandstones of the southern half of the island are 

 now seen to be unquestionably Triassic, and they are further shown 

 to have been overspread with Rhaetic, Liassic, and Upper Cretaceous 

 strata. As the volcanic vent broke through the youngest of these 

 formations, its appearance must have beeU' later than the Chalk ; 

 and thus the age of the whole complex assemblage of younger 

 eruptive masses in Arran, Avhich, including the granite, present so 

 close a petrographical resemblance to those of Mull and Skye, is 

 definitely fixed by palaeontological evidence. Of the fragmental 

 materials that fill this great vent, no doubt the main part was shot up 

 from below, but, as in some of the Carboniferous rocks-of Scotland, 

 there is evidence that large cakes and masses of the surface-rocks 

 of the country tumbled into the volcanic orifice from above. To 

 this fortunate accident we owe the proof that the Mesozoic Series 

 of Antrim once stretched north-eastward into the basin of the 

 Clyde. 



The second feature of surpassing interest in- the paper was to be 

 found in the further light now thrown on the history of the denudan 

 tion of the region. It was reasonable to suppose that at the close 

 of the deposition of the Antrim and Arran Chalk the surface of 

 that formation, whether as sea-floor or as land, stretched as a toler- 

 ably level platform, as far at least as the hills that surround the 



