470 Geological Society: — 



the microscopic examination of which shows that the pyroxenic 

 mineral, whether augitc or diallage, has frequently been con- 

 verted into a hornblendic substance, and that actinolite is found 

 filling cavities and fissures in precisely the same manner as other 

 products of alteration. The imperfect cleavage of the more compact 

 varieties is regarded by the author as in accordance with the facts 

 observed in typical slates. The metamorphism of the dolerites is 

 regarded by him as different in kind from that of the slates, and 

 caused rather by a decomposition and rearrangement of mineral 

 substances in situ than by an introduction of new material ; in 

 many cases the process of alteration may be followed step by step ; 

 and from the evidence it would appear that two rocks of similar ori- 

 gin and composition may follow two different lines of metamorphosis, 

 and thus become converted into two totally different substances ; and, 

 again, many of the metamorphic rocks have undergone a second series 

 of changes, brought about chiefly by chemical forces, and indicated 

 by the occurrence of micaceous and chloritic pseudomorphs after 

 tourmaline and an alteration (hydration) of the mica. 



With regard to the origin of the granite of Cornwall, the author 

 said that neither observation in the field nor microscopical study 

 lends any support to the notion that it is a metamorphic rock — 

 but on the contrary, that there is the clearest evidence of former 

 deep-seated volcanic action in the disturbance and alteration de- 

 scribed in his paper, and in the enormous number of granitic and 

 felsitic dykes intersecting the country for miles. The mode of oc- 

 currence of granite in other localities also seems to him to fur- 

 nish evidence in the same direction. 



14. " On the relation of the Upper Carboniferous strata of Shrop- 

 shire and Denbighshire to beds usually described as Permian." By 

 D. C. Davies, Esq., F.G.S. 



The author described sections obtained at the Ifton Rhyn Col- 

 lieries and other places in the neighbourhood, and compared these 

 with other sections displayed in different parts of England and 

 the continent, and also in Nova Scotia, and stated his conviction 

 that from the $pVorois-]imestone upwards, to and including the 

 Permian, we have one continuous series of deposits. He maintained 

 that there is no real general break in the sequence of the strata or 

 in the continuity of life, but only local unconformabilities marked 

 by equally local gaps in the succession of life. 



15. " Notes on the Physical Geography and Geology of North 

 Gippsland, Victoria." By A. W. Howitt, Esq., E.G.S. 



The earliest formation of which any trace is left in this district is 

 the Silurian — all traces of any older rocks being removed, probably 

 by the same agencies which have contorted and metamorphosed the 

 Silurian slates and sandstones. The surface of all these Silurian 

 strata shows signs of great denudation previous to the deposition of 

 the Devonian. The period that elapsed between these two epochs 



