Proceedings of the British Association. 355 
granitic and the slate systems. In support of this view, he instan- 
ced more particularly the mines in the vicinity of Marazion, where 
the lodes or mineral veins traverse lines of elvans obliquely, and 
where very rich bunches of ore have been obtained at such junc- 
tions. Indeed the miners of that part of the country are perfectly 
aware of the value of these junctions, and carry their work on as 
much as possible within their favorable influence. ‘The author di- 
rected the attention of the Section to the fact, that all the great 
mines of Cornwall are situated amid the above conditions, and to 
the advantages which geology could thus confer upon the communi- 
ty, by pointing out to them those places where the chances are fa- 
vorable to mining operations, and by inducing them to avoid those 
bubble speculations at this moment so unfortunately common.—Mr. 
Hopkins was called upon to make some observations regarding the 
direction of the fissures mentioned by Mr. De la Beche, but he did 
not enter very fully into any discussion, as he proposed, on the fol- 
lowing day, to bring the general consideration of fissures before the 
Section. He observed, shewerels that there must have been one 
great axis of disturbance, to which the smaller fissures must either 
have been parallel, or have circulated around it; indeed, Mr. De la 
Beche has supposed the great line of fissures from Blackdown to 
Cornwall had been curved by the intervening granites. He stated, 
that there must be a connexion between the width of lodes and their 
mineral contents; also, that in the production of fissures there must 
have been several periods of elevation.—Mr. Fox then mentioned 
a remarkable experiment which he had made upon the yellow sul- 
phuret of copper, having changed it by electricity into the grey sul- 
phuret. In a trough a mass of clay was placed, so as to divide it 
into two portions, in one of which was sulphate of copper in solu- 
tion, in the other dilute sulphuric acid. On the electric communi- 
cation being made by placing the yellow sulphuret in the solution of 
sulphate of copper, and a piece of zinc in the acid, the change of 
sulphuret took place, and crystals of native copper were also formed 
upon it—Mr. Fox observed, that native copper is not found in the 
mines of Cornwall combined with yellow copper, but with black 
copper ore; and that the grey ore is generally found nearer the 
surface than the yellow, and also in and near the cross courses.— 
Mr. Taylor bore testimony to the importance of geological informa- 
tion to mining agents, who now were informing themselves, not 
only in practice but in theory. He spoke of the exertions of the 
