232 Reports and Proceedings — 



3. "On the Discovery of Molluscs in the Upper Keuper at 

 Shrewley, in Warwickshire." By the Eev. P. B. Brodie, M.A., 

 F.G.S. 



Mr, E. B. Newton read a paper at the meeting of the British 

 Association at Nottingham in 1893, on some Lamellibranchs found 

 at Shrewley by the author of the present paper and Mr. Eichards. 

 In this paper details of the section where the shells were found are 

 given, and their interest and importance pointed out, no shells 

 having been previously detected anywhere in the New Eed Sand- 

 stone in this country. 



II.— March 21st, 1894.— Dr. Henry Woodward, F.E.S., President, 

 in the Chair. 



The President gave expression to the feelings of regret with 

 which the Society had received the announcement of the death of 

 Mr. William Pengelly, F.E.S., of Torquay. He had been a Fellow 

 since 1850, and had taken a leading part in the exploration of 

 Kent's Cavern, Torquay, and Brixham Cave.^ 



The following communications were read : — 



1. " On the Origin of certain Novaculites and Quartzites." By 

 Frank Eutley, Esq., F.G.S. , Lecturer on Mineralogy in the Eoyal 

 College of Science, London. 



The novaculites of Arkansas have already been admirably described 

 by Mr. Griswold in vol. iii. of the Arkansas Survey Eeport for 1890. 

 One of the characteristic microscopic features in Ouachita stone is 

 there stated to consist in the presence of numerous cavities, often of 

 sharply-defined rhombohedral form, which Mr. Griswold considers 

 to have been originally occupied by crystals of calcite or dolomite. 



The author, while admitting that the cavities were no doubt once 

 filled by the latter mineral, ventures to differ from Mi-. Griswold, 

 and some of the authorities he cites, concerning the origin of the 

 rock. Crystalline dolomites, when dissolving, become disintegrated 

 into minute but well-formed rhombohedra. As the process of 

 dissolution proceeds these crystals may become so ei'oded that the 

 rhombohedral form is no longer to be recognized. The author 

 points out that no inconsiderable proportion of the cavities in 

 Ouachita stone present irregular boundaries, such as the moulds of 

 partially eroded rhombohedra would show. He then offers a fresh 

 interpretation of these cavities, so far as the origin of the rock is 

 concerned : — 



Ist. He assumes that beds of crystalline magnesian limestone 

 have been slowly dissolved by ordinary atmospheric agency and the 

 percolation of water charged with carbonic acid or other solvent. 



2nd. That, as the limestone was being dissolved, it was at the 

 same time being replaced by silica, which enveloped minute isolated 

 crystals and groups of crystals, some perfect, others in various stages 

 of erosion. 



3rd. That the silica assumed the condition of chalcedony, its 

 specific gravity, as stated by Mr. Griswold and as determined by the 

 author, being low in comparison with that of quartz. 

 1 See Obituary, p. 238. 



