PURHAM AND NORTHUMBERLAND,

CHAPTER Y.

Deposition of Coals.—Their Duration.—TheOrigin of Coal.—Its Gases. — Accumula-tions of Fire-Damp in the Tyne and WearCollieries.

It is difficult to ascertain where beds of coalare deposited, unless there appear some signson the surface, or from fragments scatteredabout in beds of clay, though the true foun-dation may generally be depended upon afterthe secondary or blue lime-stone formation.

Mr. Bakewell, in his Geology of England,is inclined to believe that the coal strata donot extend to any considerable distance be-yond their known limits ; and observes, “ thatour prosperity and greatness as a manufac-turing nation, in a few centuries, when thepresent mines are worked out, will dependupon its determination.” * Dr. Millar, in hisedition of William’s Mineral Kingdom, givesa still more desponding account,, as to the du-ration of coals, particularly in Scotland, near

* Bakewell’s Geo. p. 351,