686 



flints ; and are sometimes accompanied by innumerable minute frag- 

 ments of other organic bodies. The size of the best-preserved spe- 

 cimens, including the prolongation, is about one-third of an inch ; 

 and the number of chambers or divisions varies in the same species. 

 Of the six species described in the paper, one had been previously 

 named, by Mr. Mantell, Spirolinites Comptoni, and the other five have 

 been named by the Marquis of Northampton, S.Murchisoni, S. Stokesii, 

 S. LyelUi, S. Mantellii, and S. Bucklandii; the author, however, 

 stated that it is exceedingly difficult to determine satisfactorily 

 specific differences, especially in such minute fossils, imbedded in 

 flint, and exposed only by accidental fracture. 



A communication was next read, entitled, " A Note to accompany 

 Specimens of Quicksilver Ore from the mine San Onofre, near the 

 town of El Doctor, Mexico." By John Taylor, Esq., Treas. G.S. 



Though quicksilver had been known for some time to exist in 

 Mexico, yet few attempts had been made to ascertain to what ex- 

 tent, till the increased prices and demand induced the directors of 

 the Real del Monte and Bolanos Mining Companies to have re- 

 searches made. Ores of that metal have, in consequence, been dis- 

 covered and traced in districts very remote from each other ; but 

 Mr. Taylor confined his remarks to the locality at which the speci- 

 mens presented to the Society were obtained. 



The ores of San Onofre are chiefly cinnabar, partly hepatic, but 

 native quicksilver occurs, and native calomel. They are stated to 

 exist in a regular vein, two or three yards in width, the gangue 

 consisting of carbonate of lime, with sulphate of barytes, and a small 

 portion of silex. It traverses a limestone hill of considerable height, 

 and appears to have been worked in former times. 



Extracts were also read from a letter addressed to John Taylor, 

 Esq., Treas. G.S., by Mr. Frederick Edmonds, explanatory of some 

 specimens of obsidian from the mountain of Real del Monte, Mex- 

 ico, collected by Mr. Frederick Edmonds, and presented to the 

 Society by Mr. Taylor. 



About half a mile from the ancient obsidian mines is the Cerro 

 de las Navajas, in which several passages may be observed from 

 an earthy felspathic rock to perfect obsidian. Although no good 

 section is exposed, the obsidian is stated to occur in irregular beds, 

 chiefly vertical, and Mr. Edmonds is of opinion, that it has been de- 

 rived from the fusion of the felspathic rock under pressure. The 

 collection presented to the Society's museum, contained a specimen 

 of calcareous tuff from the thermal springs of El Grande. 



A notice was next read of a specimen of the Oar's Rock, nine 

 miles south of Little Hampton, Sussex, by Roderick Impey Mur- 

 chison, Esq., V.P.G.S. 



The specimen consists of a calcareous grit, bearing no resemblance 

 to the Bognor rock, or other beds above the chalk, but agrees with 

 some of the beds in the green sands below that formation, or to the 



