1823.] Geological Transactions of Connuall, Vol, It. bt 



described, its formation may, perhaps, be accounted for on the 

 same principles as the formation of all true veins ; but where 

 there is a succession of floors, if junctions of lodes could be 

 satisfactorily shown at every point where they occur, it would 

 ejive us little assistance in forming a theory of their formation* 

 We have been accustomed to consider the contents of the tin 

 lodes as of posterior formation to the rocks which contain them ; 

 but here is a succession of beds, all of them connected with tin. 

 lodes (for they are always found on one or both sides of tin lodes^ 

 to which, when they are not quite close, they are united by a 

 small branch), and yet alternating with the rocks of the country, 

 which are supposed to be older than the tin lodes. It is not sur- 

 prising that the practical miner troubles himself little respecting 

 the theory of the formation of the metalliferous bodies which he 

 may discover ; but it is indeed extraordinary (as Mr. Hawkins 

 has observed in his paper on tin floors), that in a district where 

 so large a quantity of tin has been found in floors, there is not 

 more diligence and perseverance evinced in searching for those 

 deposits." 



** Formation of Sandstone, — In Pendeen Cove, which forms 

 the northern boundary of this parish, the sand consists princi- 

 pally of comminuted shells, mixed with particles of slate, and of 

 the constituent parts of granite. The chfl* which bounds the 

 cove is rather precipitous, and in one part consists of large frag- 

 ments of granite imbedded in clay and earth. The interstices 

 of this cliff are filled with sand (probably blown there from the 

 beach by high winds) ; which is exposed to the percolation of 

 water holding in solution the oxide of iron, whose cementing 

 property is well known. The sand is thus gradually becoming 

 stone, and in some parts of the cliff it has already acquired con- 

 siderable hardness.''* 



" In the Cliff near Little Bounds Mine, the same operation 

 is going forward, but the sand is more granitic than at Penden 

 Cove." 



XVI. On the Knowledge and Commerce of Tin among ancient 

 Nations. By the Rev. Samuel Greatheed. (Communicated by 

 John Dennis, Esq. MGSC.) 



This paper is entirely archaeological. 



XVII. On the Geology of St, MichaeVs Mount, By John 

 Forbes, MD. &c. 



We can only quote some concluding passages of this commu 

 nication : 



*' Much has been said respecting the relative age of different 

 granitic rocks in different countries, and among others, respect- 

 ing that of St.JMichael's Mount, which has by some late writers. 



♦ "As this sand appears in some cases to extend further than the face or the inter- 

 stices of the cliff, some have supposed a body of it to have covered the ancient surface, 

 either by the means of high winds, or other causes, before the superincumbent mass of 

 clay and granite fragments was placed there." 



e2 



