2

MODERN STEAM PRACTICE.

part of the Bristol Channel on the west coast; and the north boun-dary line extending from the south side of the river Tay in Scot­ land , westward by the south side of the Ochil Hills, to nearDumbarton upon the river Clyde; within these boundary linesNorth and South Wales are included. This area is about 260 milesin length, and on an average about 150 miles in breadth. Coalalso occurs in other formations of later geological age; but none ofthese later deposits equal in economical importance the rieh Storesof the carboniferous System in our island. Beds of coal are foundin most European countries, as also in China , India , Australia ,Japan , and Borneo ; but the coal-fields of the United States of America are by far the most extensive and richest in the world.

Boring in search of coal is an important branch of mining. Inordinary practice the boring plant consists of shearlegs, windlass,brake, brace-head, bore-rods, cutting tools, &c. Steam-enginesspecially'adapted for boring have also been devised. A very simplemethod with hollow rods combined with a force-pump was intro-duced by M. Fauvelle in 1846.

The “troubles” met with in working coal are various:—forexample, a “want” or “nip” is, as its name suggests, a part of thefield where no coal exists, or only in a very thin streak; if thisstreak is followed, however, the coal seam will again be found.“Dykes” are generally of whin, projecting from below. It rarelyhappens that the coal is either elevated or depressed by this“trouble,” but it is much burned and rendered useless for someyards on either side. A “ Step ” or “ fault ” is a dislocation, some-times of considerable magnitude, by which the strata are elevatedor depressed many fathoms. A “hitch” is of the same nature asa “ step,” but on a smaller scale. A whin bed is perhaps the worstkind of “ trouble ” to be met with, as, when found near to andparallel with a coal-seam, it renders the entire bed useless. Whena miner meets with a “step” or a “hitch” he at once knowswhether it is an “ up throw ” or a “ down throw.” If a “ hitch ” liesoff at the top, by following the rise upwards he will find the coal;if off at the bottom, he must follow the dip downwards. Althoughit is both annoying and expensive to meet with these “ troubles,”they offen serve useful purposes: “steps,” for instance, sometimeselevate the coal from a depth that would be difficult to reach byordinary means to a depth of comparatively easy working. Again,when a coal-seam is nearlv cropping out, a “ step ” is met with