CRANE.| Prospecting by Drill. 181 
form of sand pump is employed to cut through this coating 
of cement, and is called a ‘‘bailer.’’ It is furnished with a 
cast-iron nose, which is a portion of the valve which projects 
beyond the end of the bailer. 
Steam power is generally employed to lift the line of tools, 
2.e., operate the drill, although in rare instances horse power 
is used. 
The rate of drilling varies from 20 feet a day in soft lime- 
stone to 6 or 7 feet in solid flint. In ordinary ground, 10 or 
15 feet a day is considered good progress. 
Method of Casing Drill Holes. 
The depth reached by the drill hole before casing is begun 
varies greatly, on account of water and the character and 
condition of the ground. Where it is thought necessary to 
begin casing, the tool is removed and a piece of casing (ordi- 
nary wrought-iron pipe) is placed in the hole and driven 
down. A steel shoe screwed to the lower end of the casing 
is often employed to protect it from becoming cut and dented 
by striking a projecting rock. Driving blocks are employed 
to aid in forcing the casing into the hole. A driving ring is, 
however, first placed on the top of the pipe to protect it from 
the driving block. The line of tools is then lowered into the 
casing with a driving block attached to it. There are sev- 
eral forms of blocks, one of which, the one above mentioned, 
consists of two blocks of iron, clamped to the line of tools; 
another form consists of a heavy block of wood, which slides 
on guides and has a ring fastened to the top, to which is at- 
tached the drill rope. When an iron block is used, a pipe is 
fitted into the lower end, which works inside the casing, thus 
holding the block in position. In either case, when the drill 
is set in motion the block is slowly raised, then falls, acting 
as a pile-driver. 
When the top of the casing is within a few inches or a foot 
of the ground the block is removed, together with the driv- 
ing ring or plate, and drilling is resumed. When more cas- 
ing is to be added, it is fastened to the piece already in the 
ground by screwing the two together, in the ordinary way 
