48 . Miscellaneous. 



considered to lie below the workable slates of the Cambrian rocks 

 of that area, were in reality unconformable deposits of later date 

 than those slates. In 1894 (Quart. Journ. Geol. Soc, vol. l, p. 578), 

 Professor Bonney and Miss 0. A. Kaisin maintained that in no case 

 which they had examined could any valid evidence be found in favour 

 of the alleged unconformit}', and that in one (on the north-east side of 

 Llyn Padarn) which they supposed to afford the most satisfactory 

 proof of it, the facts were wholly opposed to the notion. 



The present paper is a reply to these authors, in which their 

 objections, founded on general considerations, on field observations, 

 and on microscopic examination of rock-specimens, are discussed, 

 and the author gives the results of further observations on the 

 rocks of the district. The Moel Tryfaen sections and those on each 

 side of Llyn Padarn in the Llanberis district are considered, and 

 he maintains that the post-Llanberis (using this term in the sense 

 of being after the deposition of the main workable slates) age of the 

 conglomerates which are under discussion is established ; though 

 the more he considers the correlation of these conglomerates with 

 the Bronllwyd Grits the less he likes it, and as far as the strati- 

 graphy is concerned, they may be much newer — their age is at 

 present an open question ; but of their unconformable position he 

 has no doubt. 



2. "The Geology of Lambay Island, Co. Dublin." By Messrs. 

 C. I. Gardiner, M.A., F.G.S., and S. H. Reynolds, M.A., F.G.S. 



The authors, who have previously described the neighbouring 

 district of Portraine (Quart. Journ. Geol. Soc, Dec. 1897), under- 

 took an examination of this island, with the intention of comparing 

 the rocks with those of Portraine, and of investigating the nature of 

 the rock familiar to geologists under the name of " Lambay 

 porphyry." The sedimentary rocks are similar to some of those 

 of Portraine, and are of Middle or Upper Bala age. Associated with 

 them are pyroclastic rocks and andesitic lava-flows, some of the 

 lavas having flowed beneath the sea. The sediments and volcanic 

 rocks were exposed to denudation, and a conglomerate composed of 

 their fragments was accumulated round the volcano. The " Lambay 

 porphyi-y," which has been determined as a diabase-porphyry by 

 Dr. von Lasaulx, is partly intrusive in the other rocks, but has in 

 places come to the surface as a lava- flow. 



Petrographical descriptions of the various rocks are given by the 

 authors. 



Dvcis c E Xj x. j^InTje: o US . 



New Geological Sukvey Maps. — Since our notice in the 

 Geological Magazine for 1897, p. 192, several other of the 

 Sheets of the General Map of England and Wales (scale one-inch 

 to four miles) have been issued, -printed in colours and priced 2s. Qd. 

 each. These include Sheets 2, Northumberland, etc. ; 3, Index of 

 Colours ; 4, Isle of Man ; 7, North-West Wales ; 10, Parts of South 

 Wales and North Devon ; and 13, Cornwall and the Scilly Isles 

 with part of Devon. 



