154 Geological Society : — 



crassa and Petraia crenulata, being peculiar to that formation. In 

 the flaggy slates above the Pale Slates he had found Graptolites and 

 Orthoceratites of the same species as those found in the Denbigh 

 Flags. Ho considered that the Corwen Beds were on the horizon 

 of the May-Hill or Llandovery group, and should be taken as the 

 base of the Silurian, thus including in the Pale Slates or Tarannon 

 Shale a thick series which intervened between the Corwen Beds and 

 the flaggy slates of Penyglog. 



4. " On Mineral Veins." By W. Morgan, Esq. 



The author maintained that no one theory can be accepted in 

 explanation of the formation of mineral veins, and that, whilst in 

 some cases their formation may be due to the presence of preexistent 

 fissures induced by shifting of the containing rock, in others any 

 such explanation is insufficient, as he thought the means by which 

 the sides of such fissures were kept apart could not be easily in- 

 dicated. The point upon which he especially insisted in conuexion 

 with this question was the presence of " horses " in many mineral 

 veins. He advocated the view that the walls of veins were in close 

 proximity in their earliest stage, and that the enlargement and 

 infilling of the veins took place simultaneously by the segregation 

 of materials derived from the adjacent rock, supplemented, perhaps, 

 by a tension or tendency to separation caused by slow contraction 

 of the latter. Instead of a fissure, he assumed the presence of an 

 irregular surface of least resistance or of electrical action, at which 

 the vein-matter might collect at first as a mere film. In this way, 

 he thought, the vein might increase and its walls might recede 

 simply by the aggregation of the vein-matter itself, and in general 

 in proportion to the degree of mineral saturation of the adjacent rocks. 



January 10th, 1877,— Prof. P. Martin Duncan, M.B., F.R.S., 



President, in the Chair. 

 The following communications were read : — 



1. " On gigantic Land-Tortoises and a small Freshwater Species 

 from the ossiferous caverns of Malta, together with a list of the fossil 

 Fauna, and a note on Chelonian remains from the Rock- cavities of 

 Gibraltar." By A. Leith Adams, Esq., M.B., F.R.S., F.G.S., Pro- 

 fessor of Zoology in the Royal College of Science, Dublin. 



2. " On the Corallian Rocks of England." By the Rev, J. F. 

 Blake, M.A., F.G.S., and W. H. Hudleston, Esq., M.A., F.G.S. 



The object of the paper was to describe the rock masses existing 

 betwixt the Oxford and Kimmeridge Clays. Topographically the 

 Corallian region is divided into five districts of very unequal size, 

 wholly separated from each other. The special features of each 

 district were detailed, both as regards the development, composition, 

 and fauna of the several subformations therein contained, and 

 these latter compared with their equivalents or representatives in 

 the other districts. The old names were, as far as possible, retained ; 

 but where obviously inapplicable, local names replaced them. 



In the Weymouth district (I.) one section discloses 230 feet of beds 

 between the Oxford and Kimmeridge Clays, made up in ascending 

 order of grits, clays, marls, and oolites, gritty limestones very fossili- 



