OCCURRENCE OP COPPER ORE. 335 



greatly impeded in their operations by the want of fresh water for 

 washing and dressing the raised ore. 



2. Geological Features : — The oldest rocks on the island are a series 

 of metaniorphic slates and conglomerates, probably of Palajozoic age. 

 These are exposed chiefly on the north-east side of the island. They 

 dip in various directions, but shew a general inclination towards the 

 south-west. In the accompanying sketch-section these metamorphic 

 strata are denoted by the letter A. They are traversed in places by 

 trap-dykes, partly of an amygdaloidal character, and are covered here 

 there by beds of drift gravel. At the base of the island, on the western 

 side, strata of buff-coloured sandstone crop out, and range along the 

 shore throughout almost the entire extent of this part of the coast. 

 These sandstone beds (lettered B in the section) are apparently of 

 Triassic age. They dip at a slight angle towards the south-west, and 

 must thus overlie the metamorphic strata, somewhat as depicted in 

 the section; but their extent in an easterly direction maybe greater 

 or less than is there shewn. Here and there, below the boulders on 

 the shore, they are seen on the other hand to extend in broad layers 

 beneath the sea. A bed of white or pale grey tufa (C), averaging 

 about seven or eight feet in thickness, rests conformably on these sand- 

 stones, and is succeeded by a thin layer of soft clay-like tufa (D), the 

 two presenting, in many places, no clearly discernible line of separation. 

 Finally, above the whole of these beds, a mass of columnar and sub- 

 columnar trap (B) forms a huge overflow, its surface sinking down in 

 step-like ridges towards the east, whilst on the western shore, as already 

 stated, it forms a range of high precipitous cliffs, rising almost verti- 

 cally from the sea. 



3. The Mineral Bed : — The outcrop of light coloured tufaceous rock 

 (C) referred to above, although covered up in many places by heaps of 

 detrital matter fallen from the cliff, can be traced along the face of the 

 western escarpment through(>ut a length of eight or nine miles, and it 

 extends undoubtedly beyond this distance. It is shown nowhere, how- 

 ever, in its true position ; but only along the face of the slides or ihoule- 

 ments which rest against the face of the cliffs throughout the entire 

 length of the island. As thus seen, it occupies a level much below the 

 true position of the bed. The latter must be at least thirty or forty 

 feet above high-water mark ; whereas, on the face of the slides, the 

 bed has been brought down in some places to within three or four feet 

 of the water level, and in others to about fifteen or twenty feet. In 



