138 Geological Society: — 



The sequence of the structures developed in it is made out to be as 

 follows : — First, the development of fluxion-banding ; next, the 

 formation of spherulites ; and then the setting up of a perlitic 

 structure, the fissures of which were finally sealed by the intro- 

 duction of chalcedonic matter. 



A wavy transverse banding in the spherulites is apparently due 

 to a temporary check which the fluxion-bands have exerted on the 

 development of the crystalline bundles of the spherulites. In one 

 case a spherulite has been developed prior to the formation of a 

 similar but larger one which encloses it. Some of the spherulites 

 envelop small crystals of triclinic felspar. 



The author considers it very probable that the obsidian has been 

 subjected to hydro thermal agency since its solidification, and sub- 

 sequent to the development of its perlitic structure, and gives 

 reasons for tbis view. 



May 6.— Dr. A. Geikie, F.R.S., President, in the Chair. 

 The following communications were read : — 



1. "Ona Rhaetic Section at Pylle Hill or Totter Down, Bristol." 

 By E. Wilson, Esq., F.G.S. 



In a deep railway-cutting at Pylle Hill, the Rhaetic beds, having a 

 thickness of not more than seventeen feet, are exposed between the 

 Tea-Green Marls and the Lower Lias. There is no doubt as to the 

 division between the Khaetic and Keuper beds in this section, but 

 the line of demarcation between the Rhaetic and the Lias has always 

 been a matter of uncertainty in the West of England. In con- 

 nexion with this subject the term " White Lias," as applied to beds 

 some of which are Rhaetic and others Liassic, is held to be unsatis- 

 factory. The author takes a limestone which is the equivalent of 

 the Cotham Marble as the highest Rhaetic bed in the section described. 

 He divides the Rhaetic beds of the cutting into an Upper-Rhaetic Series 

 and Avicula-contovta Shales. The intimate connexion betwixt the 

 Tea-Green Marls and the Red Marls of the Upper Keuper is well 

 displayed, whilst there is a sharp line of demarcation between the 

 former and the Avicula-contorta Shales. Most of the characteristic 

 fossils of the British Rhaetic are met with at Pylle Hill, together 

 with a few forms which are new to England, and some of these 

 possibly to science. 



A detailed section of the subdivisions of the Rhaetic and adja- 

 cent beds and a list of Rhaetic fossils found in the section are 

 given by the author. 



2. " A Microscopic Study of the Inferior Oolite of the Cotteswold 

 Hills, including the Residues insoluble in Hydrochloric Acid." By 

 Edward Wethered, Esq., F.G.S., F.C.S., F.R.M.S. 



The author gives the folloAving main divisions of the Inferior 

 Oolite of the Cotteswold Hills in descending order : — 

 Ragstones. 

 Upper Freestones. 



