1864.] r 475 [Lesley. 



The proportion of lump clay in this tunnel to unwashed ore must 

 have been, say from 5 to 10 per cent, by weight. 



The proportion of clay to ore near the surface is greater than it is 

 further down, probably because the drainage from the surface into 

 the already made ore has charged all its vacancies. But whatever 

 be the explanation, the ore-mass becomes denser and richer con- 

 tinually as one descends in the quarry, and the deepest shafts sunk 

 have left oiF in very hard, pure ore. In the limestone deposits of 

 pipe ore, the lower limit or extreme bottom plane of dissolution is 

 characterized by an accumulation of very pure and beautifully crys- 

 tallized hydrated peroxide of iron ; and all these deposits are, there- 

 fore, richest at the bottom. A mass of rock ore lies thus behind 

 the present works, and below them ; or, in other words, forming 

 the "foot-wall" or "underlay" to the deposit. This rock or hard 

 ore is struck in the galleries, and is not worked, because it re- 

 quires blasting J whereas, all the rest of the mass can be picked and 

 shovelled. In the future open quarries, this mass of ore will form 

 the richest part of the work. It is merely a more compact form of 

 brown hematite, perhaps a little more silicious than the rest. The 

 terrace above the works shows much surface ore, and on this terrace 

 come up the slates which hold the Pond-bank ore, hereafter to be 

 described. 



Again, outside, or above, or to the west of, the Home-bank belt 

 (B, of Fig. 2), there is a third belt (C), the outcrop of which is shown 

 by a sharp small ridge in a field, covered with blocks of hard ore from 

 one to two feet in diameter. The whole surface of this sloping field, 

 from the little ridge downwards, for a hundred yards, is strewed 

 with this ore, many tons of which have been collected and smelted 

 in the furnace. It is probably in connection with this ore belt that we 

 find an outcrop of almost unchanged blue carbonate of iron and lime, 

 several feet thick, mottled with groups of crystals of white calc spar, 

 and evidently, in parts, changing into honeycomb brown-hematite ore. 

 It lies with a dip of 20° towards the west. 



There are evidences of other belts further west still ; and a lime- 

 stone quarry, used for fluxing the furnace, shows a 45° reverse dip 

 (towards the east), by which we know that there is a basin, running 

 along the bottom of the slope of the mountain, and an anticlinal axis 

 west of it, bringing up the ore-bearing formations towards, and per- 

 haps to, the surface ; which is suflScient to account for the ore belts 

 just mentioned. 



This synclinal axis is the same which runs in between the Little 



