which gave
the name to the best coal. That mine is now drowned out, and, like the
great Roman Wall, at the termination of which it was sunk, and from
which it derived its name, is now an antiquity. There is now no Wallsend
coal, and the principal part of the present so-called coal comes from
the Wear, but the seam which supplied that famous pit is continued into
Durham, and that seam, or its equivalent, sends a million or two of tons
every year into London. The supply, however, in this district is rapidly
decreasing. Careful calculations have been made as to the probable
duration of this coal, of which the following is a summary. The workable
quantity of coal remaining in the ten principal seams of this coal-field
is estimated at 1,876,848,756 Newcastle chaldrons (each 35 cwt.).
Deducting losses and underground and surface waste, the total
merchantable round or good-sized coal will be 1,251,232,507 Newcastle
chaldrons. Proceeding on this estimate, formed by Mr. Grunwith in 1846,
we may arrive at the probable duration of the supplies: taking the
future annual average of coal raised from these seams to be 10,000,000
of tons--and this is under the present rate--the whole will be exhausted
in 331 years. A still later estimate was made by Mr. T.G. Hall in 1854,
and he reckoned the quantity of coal left for future use at
5,121,888,956 tons; dividing this by 14,000,000 of tons as the annual
consumption, the result would be 365 years; and should the annual demand
arrive at 20,000,000 of tons, the future supply of this famous
coal-field would continue for 256 years. The total available coal (1871)
in the British coal-fields, at depths not exceeding 4000 feet, and in
seams not less than 1 foot thick, is 90,207,285,398 tons, and taking
into account seams which may yet become available, lying under the
Permian, New Red Sandstone, and other superincumbent strata, this
estimate is increased to 146,480,000,000 of tons. This quantity, at the
present annual rate of production throughout the country--namely,
123,500,000 tons--would last 1186 years. Other estimates of various
kinds relative to our coal supply have been put forth: some have
asserted that, owing to increasing population and increasing consumption
in manufactures, it will be exhausted in 100 years, and between this
extreme and that of 1186 years there are many other conjectures and
estimates.

In the United States there are about 120,000 square miles underlaid by
known work