Some foreign writers have ascribed the great wealth possessed by this country to the coals which are here produced in such abundance, and which facilitate, in a very essential degree, nearly all its manufactures, and consequently are a means of promoting its commerce to an extent which is possessed by few other countries. All our great manufacturing towns, Birmingham, Sheffield, Leeds, Glasgow, &c. are situated either in the midst of coal districts, or in places to which coals are conveyed, with little expense, by canal carriage. Coals are principally obtained from the neighbourhood of Newcastle─upon─Tyne, Sunderland, and Whitehaven. The particular places whence they are obtained have the name of _collieries_, and the mines from which they are dug are called _pits_. The deepest of these are in Northumberland, and are worked at more than 900 feet below the surface of the earth. At Newcastle there is a coal─pit near 800 feet in depth, and which, at that depth, is wrought five miles horizontally, quite across, and beneath the bed of the river Tyne, and under the adjacent part of the county of Durham. At Whitehaven the mines are of great depth, and are extended even under the sea, to places where there is above them sufficient depth of water for ships of great burthen, and in which the miners are able sometimes to hear the roaring of the water. On the contrary, in some parts of Durham the coal lies so near the surface of the earth that the wheels of carriages lay it open, and in such quantity as to be sufficient for the use of the neighbourhood. The beds of coal are of various thicknesses, from a few inches to several feet; and in some places, it is found advantageous to work them at a very great depth, although their thickness does not exceed four or five feet. The thickest bed of English coal, of any extent, is that of the main coal in Staffordshire, which measures about thirty feet. In many places there are several beds above, and parallel to, each other, separated by strata of slate, sandstone, and other minerals. Coal is never found in chalk, and very rarely in limestone.