THE CARBONIFEROUS AGE. 
51 
When we reached tlie floor of the mine we dis¬ 
covered, by light from the tiny lamps fastened to the 
miners’ caps, that there were vacant halls and rooms 
where the coal had been taken out. In some places 
coal had been allowed to remain as pillars to keep the 
roof of the mine from falling down. Wooden posts 
had also been set up for the same purpose. In most 
parts of the mine the roof was so low that we could 
not stand upright. 
At the foot of the shaft were tramways running off 
in several directions. On these were the cars. Each 
man had his own car to fill, for which he was paid at 
a uniform price. As each car was filled, the miners 
l^ushed it along the tramway to the cage, where it was 
raised in the shaft by a hoisting engine and the coal 
dumped into the freight car. In some of the old 
mines, where mining is done at long distances from 
the foot of the shaft, tliey have mules to draw the cars. 
I noticed that the men worked with very little 
clothing on, and that each miner had a little lamp 
fastened to the forepart of his cap. This is a very in¬ 
teresting lamp invented by Sir Humphry Davy. It 
consists of a little cup containing oil, with a fine screen 
around the flame. The screen prevents the gas that 
may be in the mine from reaching the flame and thus 
causing explosions. Sometimes explosions do occur 
through carelessness when gas is accumulated in the 
mine. There is also danger to miners from fire-damp 
or choke-damp. Fire-damp is carbonic acid, which 
often collects in the mine; choke-damp is marsh gas, 
which seems to come from the coal-seams. 
