Chap. XXVI.] 
WORKING A DEPOSIT. 
553 
several small outcrops (black) arranged along the crest of the ridge. 
Possibly the outcrops will show signs of a dip, if the ore-body be a sheet- 
hke mass. Whether it does or not a series of trenches should be cut 
across the ridge at regular intervals. There is no necessity to carry them 
down to the level of the plain round the hill, but they should be carried 
down deep enough to reach rock everywhere. From this series of 
trenches it will be possible to ascertain the true strike of the ore-body, 
its dip — probably varying from point to point — , and the width at several 
points, from which an average of some value can be struck. Other 
trenches should be put across the assumed extension of the deposit on 
the plains at either end of the ridge to test the continuation of the deposit 
in both directions. One of the trenches on the hill itself might 
be cut down to a depth of at least 30 feet, in order to show that the 
deposit extends to at least this distance. It may be objected that the 
trenches shown in figure 29 are much too long, considering the width of 
the ore-band. It must be noticed, therefore, that both slopes of the 
ridge would probably be covered with talus-ore and these trenches 
would therefore indicate the quality and quantity of such ore available, 
and, moreover, reveal any subsidiary ore-bands, should such exist, as is 
not infrequently the case. It may happen that the outcrop takes the 
form of a more or less horizontal capping on the top of a hill, with 
the ore not extending down the sides. A trench or trial pit carried 
to a depth of 20 to 50 feet — or an adit driven into the edge of the 
capping some 30 feet below the top — will then probably show a 
passage down into rock that is too poor in manganese-ore to be 
workable ; and in such a case, as is so common in Mysore, it will 
probably be useless to look for ore on the low ground surrounding the 
hill, or on its sides, except in the form of detritus derived from the 
ore in situ on the top. This case is illustrated in figure 35. 
The Way to Work a Deposit. 
It is not to be supposed that the information gained in the way 
described above, valuable though it be, is necessarily all that is required 
before work can be started on rational lines. If it has revealed the 
existence of large bodies of ore near the surface, then there can be no 
doubt that the deposit should be opened up as a quarry. If the pros- 
pecting has revealed the fact that the deposits are of a superficial charac- 
ter, as in the case illustrated in figure 35, there is then also no doubt 
that the deposit is a quarrying proposition. But supposing that the opera- 
tions have shown the presence of a band of ore of good quality, but of 
III K 
