LECTURES ON POPULAR AND SCIENTIFIC SUBJECTS.

COAL AND COAL-MINES.

There are few subjects of more importance, and few less known or thought about, than our coal-mines.  Coal is one of our greatest blessings, and certainly one originating cause of England’s greatness and wealth.  It has given us a power over other nations, and vast sums of money are yearly brought to our country from abroad in exchange for the coal we send.  Nearly L17,000,000 is the representative value of the coal raised every year at the pit’s mouth, and L20,000,000 represent its mean value at the various places of consumption.  The capital invested in our coal-mining trade, apart from the value of the mines themselves, exceeds L20,000,000 sterling, and the amount of coal annually extracted from the earth is over 70,000,000 of tons.  Taking the calculation of a working miner—­J.  Ellwood, Moss Pit, near Whitehaven—­we may state, that if 68,000,000 tons were excavated from a mining gallery 6 feet high and 12 feet wide, that gallery would be not less than 5128 miles, 1090 yards, in length; or, if this amount of coal were erected in a pyramid, its square base would extend over 40 acres, and the height would be 3356 feet.

There are grounds for believing that the produce of the various coal-fields of the world does not at present much exceed 100,000,000 of tons annually, and therefore our own country contributes more than three-fifths of the total amount.  If we divide the coal-yielding counties of Britain into four classes, so as to make nearly equal amounts of produce, we find that Durham and Northumberland yield rather more every year than seven other counties, including Yorkshire.  Derbyshire, again, produces more than eight other counties, and nearly as much as the whole of North and South Wales, Scotland, and Ireland—­the yield of the latter being about 17,000,000 of tons, and that of the two first-named about 16,000,000 of tons.

In 1773 there were only 13 collieries on the Tyne, and these had increased to upwards of 30 in 1800.  The number of collieries in 1828 had increased to 41 on the Tyne, and 18 on the Wear, in all 59, producing 5,887,552 tons of coal.  The out-put of coal in Northumberland and Durham in 1854 was no less than 15,420,615 tons, and now in these two counties there are 283 collieries.  Mining began on the Tyne and continued on the Wear, where the industry has been largely developed.  There are in all about 57 different seams in the Great Northern coal-field, varying in thickness from 1 inch to 5 feet 5 inches and 6 feet, and these seams comprise an aggregate of nearly 76 feet of coal.  Taking the area of this field to be 750 square miles—­a most probable estimate—­we may classify the contents as household coal, steam coal, or those employed in steam-engine boilers, and coking coal, employed for making coke and gas.  Of household coal there is only 96 square miles out