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bed being a highly bituminous house-coal, and the remainder 
a white ash steam-coal. In no coal-field in this country 
is this so common as in the Midland Counties, the effect 
being to considerably increase the cost of production in 
separating the two qualities. 
Besides, notwithstanding the season of greatest demand 
of one quality is the season of least demand of the other, it 
is imperative to work the two together. 
In the coal-field of Northumberland and' Durham, this 
state of things is very rare ; but at least two of the most 
valuable beds, in passing from south to north, gradually and 
completely change from first-class house to first-class steam- 
coal. As, for instance, in the Hutton Seam, in the county 
of Durham, which at once yields the best house and gas-coal, 
but at different collieries ; whilst in the county of Northum- 
berland, it supplies the large bend of the well-known 
Hartley Steam Coals. 
In South Wales, the same bed is found in one place 
bituminous ; in another, semi-bituminous ; and in another, 
anthracitic. The almost universal anthracite character of the 
American coal-beds is found to change in a given direction 
to that of bituminous. 
The duration of the coal-fields of this country is a subject 
of curious interest, and has been variously estimated ; 
probably the data have not yet been obtained for arriving a1 
a satisfactory conclusion. 
The quantity of coal exhausted during the last twenty 
years has been more than doubled ; probably the future 
increase will not be in anything like the same proportion. 
The extent of unopened coal-field, required for such 
extension, has not yet been proved to exist. In all the older 
worked coal-fields, scarcely any coal area remains to be 
occupied. Much of the very best portions are already 
exhausted ; and where they are known to exist, as along the 
