TRANSACTIONS OF THE SECTIONS. 101 



0)1 {he Age of the Fehtones ami Conglomerates of the Pentland Hills. 

 By John Henderson, F.G.S.E., read hy D. J. Broavw, F.G.S.E. 



This paper was illustrated by two sections, and specimens of rocks and fossils 

 were exhibited. 



The felstones of the Pentland Hills, with their contemporaneous conglomerates 

 and sandstones, have hitherto been considered of Old Red Sandstone age, by Mur- 

 chison, McLaren, Geikie, and others. Having frequently examined the various 

 exposed sections throughout the district, and from the evidence collected, the author 

 endeavom'ed to prove that some of these felstones, conglomerates, and sandstones 

 are as new as the upper portion of the Lower Carboniferous. 



The first section referred to may be seen on the north-west side of the hills 

 at Clubbiedean, where beds of Carboniferous sandstone and shales, containing 

 Sphenopteris affinis and other well-known Carboniferous fossils, are ruptured, tilted 

 and hardened by the intrusion of the felstones ; and these intrusive felstones enclose 

 fragments of hardened shales and limestones, yielding encrinites belonging to these 

 beds, showing conclusively that these felstones are of a more recent age than the 

 overlying carboniferous. The other section referred to occurs about four miles further 

 to the south-west, at Bevelau and Plabbies How, where these supposed Old Red 

 Sandstones and Conglomerates may be seen resting on the upturned edges of the 

 Silurian rocks. In these Silurian rocks the author detected a number of felstone 

 dykes, one of which is about 30 feet broad, and may be traced iip the face of 

 Ilarehill, a distance of about 300 feet, where it is covered by horizontal beds of 

 sandstoue^the supposed Old Red — which it does not penetrate, while in the val« 

 ley to the south of Ilarehill some limestone pebbles were found enclosed in the con- 

 glomerates, which contain fossils evidently of Carboniferous age, such as Serpnda 

 paraUela, Sec, showing that these sandstones and conglomerates cannot be of Old 

 Red age as hitherto supposed. 



Now, when it is considered that the Lower Carboniferous rocks in this dis- 

 trict are everj'where broken up by intrusive felstones and greenstones, while the 

 sandstones and conglomerates of Ilarehill and the Cairnhills remain almost un- 

 touched by igneous action, and lying nearly horizontal and undisturbed, the na- 

 tural conclusion arrived at is, that these supposed Old Red Sandstones were not 

 deposited until after the igneous forces which have disturbed the Lower Carboni- 

 ferous in this district were nearly exhausted ; and the whole evidence clearly shows 

 that these supposed Old Red Sandstones, Conglomerates, and Felstones of this part 

 of the Pentland Hills must at least be as recent as the upper part of the Lower 

 Carboniferous. 



On the relative ages of tlie Granitic, Fhdonic, and Voleanic Foels of the 

 Mourne Mountains and Slieve C'rooh, Co. Doivn, Ireland. By Professor 

 Edward Hull, M.A., F.li.S., F.G.S., and William A. Teaill, B.A., of the 

 Geological Survey of Trehnd. {Commwiicated with the sanction of the Di- 

 rector-General of the Geological Survey.) 



Having referred to the bold and interesting physical features of the district, 

 which in some respects resemble those of Arran, and which had already been ob- 

 jects of investigation by Griffith*, Bergert, and Brj-ce J, the authors observed 

 that there were, as iuArrau itself, two varieties of granite. These had been 

 shown by the Rev. Professor Haughton§ to differ in composition; the gi-anite of 

 Slieve Croob (consisting of quartz, orthoclase and mica) being a " soda gi-anite," 

 and that of Mourne (consisting of quartz, orthoclase, albite, and mica) being a 

 " potash granite." l)r. Bryce had expressed an opinion that these two granites 

 belong to different epochs ||' 



» Geological Map of Ireland, 1839. 



t " On the Geological features of the North-Eastern Counties of Ireland," by J. F. 

 Berger, M.D., Trans. Geol. Soc. Loncl. 1st ser. vol. i. 



J " On the Geological Structure of the Counties of Down and Antrim," by James 

 Bryce, LL.D., Kep. Brit. Assoc. 1852, p. 42. 



§ Quart. Journ, Geol. Soc, Lond. vol. xii. p. 188, and xir. p. 300. || Siqira cit. 



