108 TECHNOLOGY. 
ward signs. We trace the head or outcrop of the bed by the shodes or 
loose fragments which have been accidentally detached from it. It is only 
in particular coal formations that the localities of beds of coal are so clearly 
indicated as to furnish sufficient grounds for working the mine. If the 
miner has found the locality of a bed or vein, he must closely examine 
the region around in order to judge of the changes the formation has under- 
gone. Springs which contain hydrochlorate of potash in solution are 
usually indications of the presence of beds of coal. Naphtha and asphaltum 
springs indicate also localities of coal; jets of carbonic acid, or carburetted 
or sulphuretted hydrogen gas, frequently mdicate beds of coal, as well as 
masses of mineral salt. 
If any one, by means of any of the indications above-mentioned, has 
come upon the outcrop of a bed or vein, he must attempt to uncover and 
display it. He must examine its dips and determine its strike by those 
parts which are uncovered, and also determine its extent by sinking pits in 
the vicinity of the bed or vein, and driving transversely to intersect it. The 
experimental work should be carried on until the miner shall consider him- 
self justified in commencing the real working of the mine. In those cases 
in which saline or gaseous exhalations serve as indications of the presence 
of beds of minerals, Bortye is the most suitable experimental work. 
The earth-borer, or auger, is an instrument for boring, in any soil, holes 
of small diameter, in order that we may not be obliged to sink a shaft or 
drive a level to learn the nature of the soil. We have already spoken of 
Boring when treating of Artesian Wells (Vol. I. p. 626), and have repre- 
sented the principal boring tools, so that we shall here content ourselves 
with a short enumeration of the same. 
An auger consists of an upper piece, which always remains above the 
hole bored, and of a lower piece, or the auger proper, which takes hold of 
the bottom of the auger-hole and its sides. The middle piece, or shaft, 
unites the two pieces above named, according to the depth of the auger- 
hole. The auger is suspended by means of the upper piece to the rope in 
the boring-frame, and must be so arranged that a person ean turn the auger 
without twisting the rope. The middle piece or shaft is cylindrical, octa- 
gonal, or square. The last form is best, because it 1s cheapest and at the 
same time admits of the use of holes for inserting handspikes. The size is 
according to the depth of the hole to be bored. The diameter is usually 
14 lines, but for the greatest depths is as much as 21 lines. Its length is 
from 16 to 19 ft. Each end is enlarged for the purpose of joining the 
middle piece to the parts above and below. The most common method of 
uniting the different pieces of the auger is by means of a male and female 
screw with triangular threads. The lower end contains the female screw, 
the upper the male, which is from an inch and a quarter to an inch and a 
half indiameter. This mode of joining is not so good as the joining by means 
of a tongue and groove, which admits of turning the auger in all directions. 
The boring part of the auger has different forms according to the strata 
of rocks which are to be penetrated. The chisel auger serves for boring 
through loose and disjointed strata, like sandstone, &c. In order to fasten 
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