236 OCCURRENCE OF COPPER ORE. 



these slides, also, the bed has been more or less broken up, and has 

 been made to dip inwards or towards the east, as shewn in the accom- 

 panying section, whilst the true inclination is evidently in the opposite 

 direction. 



This tufaceous bed carries small patches and stains of earthy mala- 

 chite or green carbonate of copper apparently throughout its entire 

 length; and where the bed has been excavated to the extent of a few 

 feet, these stains and earthy masses are seen to have arisen from the 

 partial decomposition of small strings and bunches of copper glance or 

 sulphide of copper, one of the richest ores of that metal. Only two 

 excavations, however, have at present been carried into the bed, and 

 neither of these reaches the solid or unfractured rock. But these exca- 

 vations are about five miles apart, and here and there, on the interven- 

 ing stretch of shore, pieces of the rock, thickly charged with malachite, 

 or shewing strings of copper glance, occur amongst the detrital matters 

 dislodged from above. It may be fairly concluded, therefore, that the 

 bed carries ore of this character throughout the entire length of its 

 outcrop; but this cannot be absolutely proved without undertaking 

 regular exploratory work, as a comparatively slight shock at the foot 

 of the cliff is sufl&cient to bring down many tons of rock and stone. 

 This tendency to fall is in great part due to the face of the cliff being 

 composed of vertical columns of basalt, which separate readily at the 

 partings. On the actual face of the outcrop, the show is in many 

 places very poor. Here and there, for the space of a couple of fathoms 

 or more, merely a few faint stains are observable, but in other places 

 distinct patches of malachite occur. The ore appears to have been 

 greatly decomposed near the face of the outcrop, partly, perhaps, by 

 the action of sea-water; and it may thus, in course of time, have been 

 gradually dissolved out or washed away. The water which infiltrates 

 in places through the bed, holds evident traces of copper salts, as a 

 film of metallic copper has been found on picks and hammers acci- 

 dentally left in contact with it. The first three or four, or perhaps five 

 feet of the bed (measured from the face of the outcrop generally,) will 

 not certainly give an average yield of one per cent, of metal ; but at a 

 distance of ten or twelve feet, if the present excavations may be taken 

 as a criterion, a yield of at least five or six per cent, may be anticipated 

 (see Assays in § 4). Copper glance contains normally 79-8 per cent, 

 of metallic copper: the presence of a comparatively small amount is 

 suflScient, therefore, to form a paying ore. Malachite, also, although a 



