DURHAM AND NORTHUMBERLAND. 31

good ventilation ; but should this be deficient,it may explode on ignition when the wholehas broke forth into the mine, as the accumu-lation would be too great, and overcharge theatmospheric air.

There is much difference in the appearanceof gas-yielding coal; but, generally speaking,the Durham and Northumberland coal yieldsabundance: and at this time much danger issuspended over these immense works, fromtheir astonishing extent, and the great increaseof inflammable principle which this extent na-turally produces. In part of the Hutton Seam,for instance, which has been worked out, thegas has become so powerful that nothing willcontain it; on this seam being worked out,the shafts and staples * were stopped up to thenext seam above it, by means of strong scaffold-ing, clay, straw, earth, &c. seven fathoms inthickness, and the water suffered to drain intoit as an old waste. The water has now accu-mulated in considerable quantities, and having

* A kind of smaller shaft cut through from one stratumof coal to another in different parts of a mine, for thepurposes of ventilation, and for the passage of miners.I descended one of these by means of a rope ladderwith wooden staves, and which was hung on a post atthe top of the staple; the bottom of this staple was 12 $fathoms from the surface.