pratt.] METHODS OF MINING. 73 
lily only where it has been associated with peridotite rocks. These 
rocks, as will be shown later, present certain difficulties which, if not 
overcome, will cause considerable delay and danger in mining. The 
emery occurring in amphibolite presents these difficulties in only a 
slight degree. 
Nearly all of the peridotite formations in which the corundum 
deposits occur are bold outcrops on the mountain sides and hilltops, 
having almost perfeel natural drainage. At all the localities where 
there has been no mining the little prospecting has been usually by 
means of open cuts supplemented by tunnels. While at first mining 
by means of cuts may seem to be the most advantageous, it is soon 
found to be the cause of considerable extra expense. These nils, or 
any other openings made over the surface of the peridotite, offer a 
much greater opportunity for surface water and frost to penetrate the 
mass of the rock formal ion. These rocks are more or less seamed or 
cracked, usually to the depth thai alteration can extend, ami thus 
offer opporl unit ies for the infill rat ion of water. As most of tin- alter- 
ation products of this peridotite formation are slippery hydrous mag- 
nesium minerals, such as serpentine and talc ami as these are devel- 
oped in the seams and cracks of the peridotite, anything thai is done 
to disturb them will make them very liable to slip. At the Corundum 
Hill mine there are large masses of peridol Lte thai have become loos- 
ened and gradually slipped down and closed up some of the tunnels, 
and there is constanl danger thai fragments of the rock will fall into 
the cuts and some of the tunnels. At the Laurel Creek mine, a mass 
of peridotite with soil, etc., nearly a 200-foo1 cube, has become loos- 
ened and slipped downward, effectually closing up the tunnel and 
shaft of the Big vein. 
In mining corundum associated with peridotite rocks it is therefore 
advisable not to break the surface of the formation any more than is 
absolutely necessary and to do no work at all along the contact by 
means of open cuts, but to confine the mining to a system of tunnels 
and shafts. This method of mining will be found the cheapest in the 
end. Then, again, all the tunnels and shafts should be well timbered 
and the mine kept as thoroughly drained as possible. 
A large amount of the material that must be handled is easily 
worked with pick and shovel, as it consists of the ciystals and frag- 
ments of corundum in the zone of chlorite and vermiculite. In those 
veins in which the corundum is associated with feldspar, as at Laurel 
Creek and Buck Creek, and those where there is considerable amphi- 
bole or enstatite, as at Corundum Hill, blasting is necessary. Most of 
the corundum deposits in peridotite are so located that there need be 
but little hoisting of the ore for some time. By drifting from a shaft 
at tin 1 upper end of a tunnel that has been run into the vein at the 
lowest level possible the ore can be removed with a. minimum of hoist- 
ing and the mine will be kept dry. 
If the mill is located some distance from the mine and a line of 
