Mr. J. J. Murphy on the Cause of the Glacial Climate. 387 



rock, striking about N.E. and S.W., and dipping generally to the 

 N.W. at a high angle. The series exhibits little disturbance, but 

 great lithological variation ; on the whole felspar predominates in 

 the lower part, whilst hornblende increases in quantity as we ascend 

 in the section. The felstone and talc schist, more especially the 

 former, contain eminently auriferous lodes ; the gneiss contains dis- 

 seminated gold, and that to the north of Upata a rich deposit of red 

 haematite and a few intrusions of greenstone. 



This metamorphic series was considered to be contemporaneous 

 with a similar series constituting the Littoral Cordilleras of North 

 Venezuela, the praecretaceous age of which is proved by their being 

 overlain by unaltered Neocomian beds. Indulging in speculation 

 as to the age of these auriferous rocks, the author sought, by ana- 

 logy of their mineral contents and their lithological similarity to 

 certain auriferous and associated strata in Bolivia, to establish their 

 Silurian age. 



Skirting the Orinoco and abutting against the escarpment of the 

 Itacama Mountains, were described the " Llanos " sandstones and 

 conglomerates, derived from the metamorphic series. These beds, 

 which were referred to the Upper Miocene, are in their easterly 

 extension lignitiferous and asphaltic ; and as the basin of the Ori- 

 noco is excavated in them, it was contended that the present river 

 could have played no part in the accumulation of the materials 

 from which the asphaltic deposits have been supposed to have 

 originated. 



5. " On the Nature and Cause of the Glacial Climate." By Jos. 

 John Murphy, Esq., E.G.S. 



The author cited the conclusions arrived at by Mr. Croll as to the 

 causes of glacial climate, and stated his agreement with them, ex- 

 cept in one instance : he maintained, in opposition to Mr. Croll, that 

 the glaciated hemisphere must be that in which the summer occurs 

 in apKelio during the period of greatest eccentricity of the earth's 

 orbit. He showed that a cool summer had more to do with the 

 prevalence of glacial conditions than a cold winter, and referred to 

 several phenomena furnishing arguments in favour of his opinion. 



June 23rd, 1869.— Prof. T. H. Huxley, LL.D., F.R.S., President, 

 in the Chair. 



The following communications were read: — 



1. " On two new Species of Gyrodus." By Sir Philip de Malpas 

 Grey Egerton, Bart, M.P., F.R.S., V.P.G.S. 



The author remarked upon the characters of the genus Gyrodus, 

 of which he described two new species, namely : — G. Goweri, from 

 a deposit of Oolitic age on the east coast of Sutherland, having the 

 scales covered with a somewhat reticulated raised pattern, inter- 

 spersed with granules ; and G. coccoderma, from the Kimmeridge 

 Clay of Kimmeridge, having the scales adorned with a multitude of 

 symmetrical granules which show no tendency to coalesce. The 

 author also described a vomer of Sphcerodus gigas, bearing teeth of 

 the form usual in that genus, and remarked that this specimen esta- 

 blished the validity of the genus Sphcerodus. 



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