236 Reports and Proceedings — Geological Society of London. 



facts. Exception is taken to certain physical processes postulated 

 by Professor Iddings in a recent memoir, but with his earlier work 

 the present writer is substantially in agreement. 



In the second part of the paper direct comparison is drawn between 

 the structures exhibited by the hollow spherulites from Obsidian 

 Cliff and those of examples from Shropshire, Jersey, and other 

 localities. Attention is called to the presence in the latter of 

 quartzose amygdaloids, crescentic in shape, and having a relation to 

 the edge of the nodule. Sometimes a series of such are found 

 parallel one to the other, not infrequently (at Wrockwardine) 

 becoming more or less completely circular. Projecting into such an 

 amygdaloid, or occupying an end, we find in many instances a 

 network of felspathic fibres comparable with the fibrous structure 

 which characterizes the American examples. 



A description is given of a series of rocks from Boulay Bay, once 

 very vesicular, and containing the remains of crystals — probably 

 felspars — analogous to the crystals found encrusting the cavities of 

 lithophysEe from Obsidian Cliff. Traces of a mineral which resembles 

 the tridymite from the latter locality are described from Wrock- 

 wardine. 



Taking into consideration the resemblances between the hollow 

 spherulites of the Yellowstone region and those of Great Britain, 

 the conclusion is drawn that the hypothesis of corrosion is as 

 inapplicable to the latter as to the former. On the contrary, the 

 author believes that the cavities of the spherulites are the result of 

 the hydrous state of the magma. 



II.— March 20, 1901.— J. J. H. Teall, Esq., M.A., V.P.R.S., President, 



in the Chair. 



Mr. H. B. Woodward called attention to a polished slab of 

 Landscape Marble, or Cotham Stone, from the Rhfetic Beds near 

 Bristol, which had kindly been lent for exhibition by Mr. Frederick 

 James, Curator of the Maidstone Museum. The specimen showed 

 that after the arborescent markings had been produced in the soft 

 mud, some irregular and partial solidification took place in the 

 upper layers of the deposit ; and then during contraction a kind of 

 -subsidence occurred of the upper and harder portions into the 

 lower and softer materials. This subsidence was accompanied by 

 a breaking up of the harder portions, suggesting a comparison (in 

 miniature) with ' broken beds ' and even crush-conglomerates. The 

 specimen was of considerable interest as illustrating the mechanical 

 changes produced during solidification. 



The following communications were read : — 



1. " On a Remarkable Volcanic Vent of Tertiary Age in the Island 

 of Arran, enclosing Mesozoic Fossiliferous Rocks." 

 (Communicated by permission of the Director -General of H.M. Geological Survey.) 

 Part I. — " On the Geological Structure." By Benjamin Neeve Peach, 

 Esq., F.R.S., L. & E., F.G.S., & William Gunu, Esq., F.G.S. 



The rocks which form the subject of this paper cover an area of 

 a,bout 7 or 8 square miles, and culminate in Ard Bheinn A'Chruach 



