264 NEW ZEALAND NATURE-STUDY BOOK 
manufacture of certain kinds of pottery. The fire-clay 
was originally the soil in which grew the plants subse- 
quently converted into Coal. It is frequently penetrated 
by roots, which, in some cases, can be traced back to the 
fossil trees occurring in the seams. 
Sometimes the Coal-seams outcrop at the surface ; but in 
most cases they are buried to a considerable depth. When 
this occurs, they are reached either by putting in drives or 
sinking shafts. The Coal is hewn out of the seams and 
hauled to the surface. A deposit of the mineral, worked in 
this way, is known as a Coal-mine. 
The mineral Coal is found in most countries, Immense 
Coal-fields occur in England. Indeed, it is to the presence 
of these that she owes much of her prosperity. In New 
Zealand extensive deposits are found in the Auckland, 
Nelson, and Otago provinces, where mining is profitably 
carried on. 
Uses.—Coal is one of the most valuable of all the 
minerals. It is used as fuel in the production of steam, and 
artificial heat for domestic purposes, and is also employed 
in smelting metals, baking clay, and the manufacture of 
gas. . 
Coal Gas.—-Grind up some Coal and place it in the 
| bowl of a tobacco 
pipe, as shown, being 
careful to cover the 
top of the bowl with 
clay so as to prevent 
the access of air. 
Heat the base of the 
bowl, and _ observe 
the yellow gas issu- 
ing from the end of 
the pipe. After a 
Fig. 148.—Pipe over gas flame. 
