1815.] Geological Socieii/, 311 



force originally impressed upon it, and to the degree of resistance 

 offered by the varying thickness and solidity of the stratified rocks. 



A letter from the Rev. Richard Hennah, jun., dated Jan. 19, 

 1815, was read. 



The object of this letter is to state that, in addition to the infor- 

 mation contained in the former letters of this gentleman, (read 

 Nov. 18, 1814,) concerning the occurrence of organic remains in 

 the Plymouth lime-stone, he has recently found many well-defined 

 shells of the genus turbo, and of other genera, at the east end of 

 the Hoe under the citadel j and also fragments of shells in a quarry 

 at Cat- down. 



A memoir on the native oxide of uranium of Cornwall, by W, 

 Phillips, Esq. M. G. S. was read. 



Uranite in green tabular transparent crj'stals, imbedded in fer- 

 ruginous quartz, has been found by Mr. Phillips, at Carharrock, 

 near St. Die. It has also been found by him in very minute crys- 

 tals, varying in form and colour, and accompanied by pitch blende, 

 at Tincroft mine near Redrutii; also in well defined crystals, and 

 accompanied by pitch blende, at Tol Came mine. 



At Huel Jewel this mineral occurs on red copper ore; and in a 

 single instance has been found on the surface of Wavellite from 

 Stenna gwyn near St. Austle. Specimens of extraordinary beauty 

 have been discovered within the last three or four years at Gannis 

 lake copper mine near Callington, on decomposed granite. 



The larger crystals of this mineral are all deeply striated ; and 

 even the most minute ores, although seemingly well defined, are 

 ■not capable of being accurately measured by the reflecting gonio- 

 meter. From some very satisfactory clcaragcs which Mr. Phillips 

 has obtained, it appears to have natural joints parallel to the lateral 

 faces, and to the two diagonals of a tetrahedral prism. 



The p>aper concludes with a description, illustrated by drawings, 

 of 46 varieties of crystalline form. 



A paper, entitled Supplementary Observations on Quartz Rocks, 

 made in 1814, by Dr. Maccullodi, was read. 



This rock forms the larger portion of the great valley of the 

 Tunnel, where it alternates with micaceous and with argillaceous 

 schist, with lime-stone, and with porphyry. It may be observed 

 passing insensibly into granite, and, when it alternates with mica- 

 slate, the proportion of quart/ rock will be found to prevail in the 

 vicinity of granite ; and that of niica-slate at a distance from the 

 granite. Jn Ben Gloe it occurs iticurvated and contorted; and on 

 Caiin Gower are some beds consisting wholly of large and small 

 rounded pebbles. In Mar forest it alternates with large incomplete 

 garnets. In Glen Tilt it pn-sents a finely laminated structure, like 

 the schistose sand-stones of tiie coitl strata, and is divided by natu- 

 ral joints into rhoniboidal tables. In Ben Gloe it occurs of a beau- 

 tiful pink colour ; and in Glen Fernat it is mixed with scales of 

 mica forming an avantuiine capable of receiving a good polish. 



March y. — The reading of Mr. Jlorner's paper on tiie Geology 

 of the South Western part of Somersetshire was begun. 



