«36 REPORT— 1901. 



FRIDAY, SEPTEMBER 13. 



The following Papers were read : — 



1. Time Inter iiah in the Volcanic History of the Inner Hehridea. 

 By Sir Archibald Geikie, D.C.L., F.B.S. 



2. The Sequence of the Tertiary Igneous Eruptions in Skye} 

 By Alfred Harker, M.A., F.G.S. 



As regards the sequence of the varied succession of Tertiary igneous eruptions, 

 the isle of Skye may probably be taken as a type of the whole British area. 

 Igneous activity passed successively through three phases: the volcanic, the 

 plutonic, and the phase of minor intrusions. It is important further to recognise 

 two parallel series of events, the regional and the local ; the former of very wide 

 extension, the latter connected with certain deiinite foci, one of which was situated 

 in Central Shye. The groups of rocks having a regional distribution are all of 

 basic composition, but the local groups exhibit much greater diversity. During 

 the plutonic phase, when regional activity was in abeyance, the successive groups 

 of intrusions at the Skye centre followed an order of increasing acidity (ultrabasic, 

 basic, acid) ; but for the local groups of the succeeding phase of minor intrusions 

 this order was reversed. 



3. On the Relations of the Old Red Sandstone of North-west Ireland to 

 the adjacent Metamorjjhic Rocks, and its similarity to the Torridon 

 Rocks of Sutherland. By Alex. McHenry and Jas. R. Kilroe. 



The Old Red Sandstone of North-west Ireland has been affected by earth 

 stresses in pre-Carboniferous times, resulting in a system of reverse faults and 

 thrust-planes. This system strikes north north-eastward, and if continued, as is 

 probable, should be represented in the region of Sutherland and Ross. We sug- 

 gest it is found in the great system of thrusts which affects the structure of the 

 North-west Highlands. 



The long-recognised resemblance of the Torridon Rocks in Sutherland to the 

 Old Red Sandstone, especially, as we hold, to the Old Red of Donegal, Tyrone, 

 and Mayo — both as regards its general lithological characters, contained pebbles 

 and relations to the underlying metamorphic rocks, the disposition of the strata, 

 their striking horizontality in places, and strong resemblance of physical 

 features — is fairly suggestive of the contemporaneity of the two groups, a view 

 rendered quite possible by the above-mentioned system of N.N.E. thrust-planes. 



Our post-Old Red thrust-planes are in places lined with broken-up debris, in 

 some cases strongly resembling conglomerates of deposition, and giving to the 

 older rocks apseudo base, apparently derived from the newer rocks, or newer and 

 older mingled. This, we suggest, may be the case with the base of the Durness 

 series, and the comparatively friable nature of the sandstone and conglomerates 

 would admit of easy movement en masse of the lower members of the Durness 

 series in overriding the Torridon when once a thrust-plane became initiated. 



4. On the Relation of the Silurian and Ordovician Rocks of North-ivest 

 Ireland to the Great Metamorphic Series. By Jas. 11. Kilroe and 

 Alex. McHenry. 



Upper Silurian rocks, as high as Wenlock, have been metamorphosed along 

 the Croagh Patrick range, which led to their inclusion in the great metamorphic 



' Pi>blished in full in the Ofolo^ical Magazine, November 1901, pp. 506-509, 



