CiiAP. XXVI.] 
MI>"ING V. QUARRTING. 
540 
it up to a marketable grade ; whilst at depths below this 50 to 100 feet, 
but otherwise under the same conditions, it might not be possible to 
work ere that was not of fairly high grade, and required mechanical 
treatment to render it marketable. Some manganese-ore deposits 
contain bands of ore requiring mechanical treatment to render them 
fit for the market, alternating with bands of ore not requiring such 
mechanical treatment. In such a case if an average sample of the 
whole width of the ore-body were taken at a depth of 100 feet, the assay 
result might indicate that the deposit could not be profitably worked 
at such a depth. ^Miilst if the poor and rich ore were analysed separately 
it might turn out that it would pay to work the deposit at this depth 
bv rejecting the lower grade ore. It is possible to imagine the case of two 
manganese-ore deposits, the average ore of which taken from a depth 
of 100 feet assayed 35 per cent, manganese in each case. But on account 
of the ore of one being uniformly of 35 per cent, grade throughout, 
a considerable proportion of the remainder being quartz, it might be 
unprofitable to work it, on account of the cost of treating the ore mecha- 
nically in order to fit it for the market. On the other hand, the 
other deposit, being composed of bands of ore of variable composition, 
some as high as 50 per cent, manganese, and some as low as 20 to 
30 per cent, manganese, might possibly be workable at a profit by saying 
only the higher grade ore, and rejecting the remainder, so as to avoid 
the cost of mechanical concentration. 
4. The character of the ' country ' or enclo.sing rock of the ore 
deposit is also a matter of considerable import- 
oft'he deposit '-ou^tn ^nce. In cases where it is extremely soft and 
wet, as in the case of the Hthomargic ' country ' 
of Kodur and other mines in the Yizagapatam district, it might be a matter 
of extreme difficulty and danger, with very high working costs, to mine 
the deeper portions of the deposit ; whilst on account of the ex- 
treme softness of the ' country ' it might be possible, by carrjdng 
out an enormous amount of deadwork, to work opencast to a much 
greater depth than would be passible ^vith hard ' country' , at a cost 
much lower than that of true mining ; the quarrj- would be very much 
wider than the width of the ore-body, and would have its sides stepped 
on account of the softness of the ' country ' ; and the soft ' country ' 
would be removed in slices as the quarry was constantly deepened. 
Such is the practice that has been followed in the case of the Kodur 
quarry in Yizagapatam. which has now reached a depth of about 100 
feet below the original surface of the plains. Such a method of work 
