Coal Mines of Virginia. 129 
or shut, by means of a close door. As the old works are very 
near the fire, the air in them becomes very much rarified by 
the heat; and probably a considerable portion of it is consum- 
ed, (as the principal pabulum for the combustion,) and a_par- 
tial vacuum is produced. When the air, in their present works, 
therefore, becomes impure, they open the door, and a strong 
current rushes into the old works ; its place is again supplied 
with fresh air through the shafts. Previous to the adoption 
of this mode of ventilation, they experienced great inconve- 
nience from carbonic acid gas; and some of the workmen had 
been killed by an explosion of carburetted hydrogen gas, Since 
this mode has been adopted, they have experienced no incon- 
Venience at all from noxious gases. On inquiry, I was told 
that the substances passed through, in getting to the coal, va- 
tied in the different pits. As far, however, as 1 could learn 
by inquiry, and an examination of the heaps of rubbish, the 
following substances, in the order in which they stand, have 
been found in Heth’s pits :—mould, clay, gravel, fuller’s earth, 
sandstone, (at first extremel y coarse and friable, but becoming 
more compact and hard, and having an appearance somewhat 
stratified as they descended,) gray and bluish clay slate, hard 
bluish sandstone, shale, or, as they term it, shiver, white mica- 
“sous sandstone, extremely hard; blue slate and shale inter- 
mixed, black slate, and then the coal. The depth of these stra- 
‘adifered so much in different pits, that their individual thick- 
hess could not be ascertained. Vegetable impressions are 
very Common in the slate next the coal; and they have found 
the impression of a fish. Pieces of pure charcoal, in the form 
. sticks, or logs, are frequently found in or omthe coal. In 
Sinking one of the pits they met with a perpendicular column, 
8 inches in diameter, extending through the slate into the coal ; 
m all about 50 feet. Its surface was distinctly serrated, and 
at 'ntervals of about two inches it appeared jointed, breaking 
‘asily at the joints. For the want of a better name I myst call 
ta“ lusus haturee ;”” for it is neither clay-slate nor mica-slate, 
"or shale, nor sandstone, but appears to be composed of them 
* Masses of a black oxide of iron are sometimes found in 
the slate ; and from its weight and hardness the miners very 
91. L...No, 2. 17 
