1822.] Royal Geological Society of Cornwall. 313 



black carbonaceous powder ; while that from soft steel and soft 

 alloys was in much greater abundance and plambagenous. 



When the alloys were acted on by dilute sulphuric acid, the 

 residuum boiled in the acid, and the powder left acted on by 

 nitric acid, this powder, whenever the alloy contained a metal 

 insoluble in nitric acid, was either detonating or strongly defla- 

 grating ; whereas, when the alloying metal was soluble in nitric 

 acid, the powder was entirely dissolved, and nothing of a similar 

 nature produced. 



It was observed that the metals platinum and rhodium combine 

 with steel in every proportion, forming with some of the higher 

 proportions beautiful compounds, the colour favourable for me- 

 tallic mirrors, and not subject to tarnish on exposure to the 

 atmosphere. Steel with the last named metal was particularly 

 noticed. 



ROYAL GEOLOGICAL SOCIETY OF CORNWALL. 



The following papers have been read since the last Report : 



On the Mineral Productions and Geology of the Parish of St. 

 Just, By Joseph Carne, Esq. FRS. MRIA. Member of the 

 Society. 



On some Advantages which Cornwall possesses for the Study 

 of Geology, and on the Use which may be made of them. By 

 John Hawkins, Esq. FRS. Honorary Member of the Society. 



On Stratification, and on the external Configuration of the 

 Granite of Cornwall. By John Forbes, MD. Secretary of the 

 Society. 



On the Gwithian Sands. By Henry Boase, Esq. Treasurer of 

 the Society. 



On the Slaty Rocks of Cornwall, more particularly on those 

 usually denominated Killas. By Dr. Forbes. 



Additional Observations on the Temperature of Mines. By 

 R. W. Fox, Esq. Member of the Society. 



Notice on the Geology of Nice. By G. C. Fox, Esq. Member 

 of the Society. 



Some Account of the South American Mines. By the Rev. 

 John Trevenen. 



Some Account of the Mines of Pasco, in South America. By 

 Mr. Richard Hodge. Communicated, with additional Obser- 

 vations, by Sir Christopher Hawkins, Bart. MP. FRS. Member 

 of the Society. 



Some Account of the external Features (natural and artificial) 

 of a Country, from which its Geological Structure may be 

 inferred. By Dr. Forbes. 



Notice of the Quantity of Copper raised in Great Britain and 

 Ireland in the Year ending June, 1821. By Mr. Alfred Jenkyn, 

 Member of the Society. 



Notice of the Quantity of Tin raised in Cornwall in the Ye?^r 

 ending June, 1821 , By Joseph Carne, Esq. FRS. 



