Geological Society of London. 237 



masses Hthologically similar to two distinct periods; and (3) the 

 OGcui-rence of conglomerates similar to those which are elsewhere 

 admitted to be basal Cambrian. But in addition to these minor 

 difficulties, the theory of a Mid-Cambrian age for the above-named 

 lava is shown to be without foundation. It was supposed that in 

 the Bryn Efail quarry the slaty rocks of the district immediately to 

 the north could be seen in contact with, and altered by, this lava. 

 The author shows that no slate occurs in the quarry, a diabase 

 having apparently been mistaken for it, and that there is no grit in 

 the section which would aiford any support to the new theory. The 

 author concludes that the Llyn Padarn felsite is probably, as classed 

 by Dr. Hicks and Prof. Bonney, of pre-Cambrian age. As regards 

 the country to the north, the ai'gument for the new arrangement 

 was based mainly on the interpretation of the Bryn Efail rocks; 

 but as this is seen to be erroneous, the section founded on it does not 

 appear preferable in any way to that published by the Geological 

 Survey. 



3. "On a Labyrinthodont Skull from the Kilkenny Coal-measures." 

 By E. Lydekker, Esq., B.A., F.G.S. 



The author describes a skull from Jarrow Colliery, which he 

 refers to Ichthyerpelvm, and names I. hibernicum, giving reasons for 

 its specific distinctness from I. (Ei-petocephalvs) rugosum, Huxley. 

 He compares it with allied forms, and believes that it is a member 

 of the group Brachyopina of Miall, and if so that we have a number 

 of forms belonging to a type which is unknown above the base of 

 the Permian in Europe, but which survived to later times in the 

 Indian, Australian, and Ethiopian regions. 



II.— March 11, 1891.— Dr. A. Geikie, F.R.S., President, in the 

 Chair. — The following communications were read : — 



1. " Manod and the Moelwyns." By A. V. Jennings, Esq., F.L.S., 

 F.G.S., and G. J. Williams, Esq., F.G.S. 



The area described by the authors is on the N. side of the 

 Merionethshire anticlinal of Lower Cambrian rocks, and contains 

 Lingula flags, Tremadoc and Arenig rocks. The authors correct what 

 they think is an inaccuracy of some importance in the correlation 

 of beds in different parts of the range, as interpreted in the map 

 and memoir of the Geological Survey, and trace with greater com- 

 pleteness the position and constancy of the beds of slate in the 

 Arenig series — a point of considerable local and practical importance 

 to those engaged in slate-quarrying. They offer also what seems 

 to them to be conclusive evidence to show the intrusive nature 

 of the great crystalline mass known as the syenite of Tan-y-Grisiau, 

 and to its intrusion are due, in their opinion, the peculiar physical 

 characteristics of the surrounding country. Though in the immediate 

 neighbourhood of Festiniog there is no direct evidence of unconformity 

 between the Tremadoc and Ai'enig series, it seems probable that an 

 unconformity does exist ; for when traced toward the west the 

 Tremadoc beds thin out and the Lingula flags are overlain by 

 Graptolite-bearing slates of Arenig age, while eastward, near Llyn 



