230 Mr. M. Dunn on the Sinking of Preston Grange Engine Pit. 



of 2 or 3 feet. This species of tubbing answered well enough for the 

 very top of the pit, but, where considerable pressure was expected, it 

 was necessary to support such planking by an internal tier of cribs, 

 ranging, according to circumstances, at from 6 to 20 inches from each 

 other and covered in front by a facing of deal. 



With this description of tubbing was effected the winning of Heb- 

 burn, Jarrow, South Shields, and other collieries, in this neighbourhood, 

 about and since the year 1790, in which collieries some of the tubs are 

 sustaining water under a pressure of 40 fathoms, or 1001b. per square 

 inch. 



The first cast-iron tubbing was introduced by the late Mr. Barnes, 

 at the King Pit, Walker Colliery, about the year 1795, but at that time, 

 and for several years afterwards, it consisted of entire circles the full 

 size of the shaft ; and, however useful it might be in passing through 

 sands, &c, near the surface, it could not be applied in the main body 

 of the shaft, after the pumps and other engine furniture became ne- 

 cessary. 



The first instance of the application of cast-iron tubbing, by forming 

 it into convenient segments, was in the winning of Percy Main Colliery, 

 in 1796-7, under the direction of Mr. Buddle, to whose scientific and 

 professional exertions this mining district is indebted for so many of its 

 greatest improvements. At this period, the flanches were bolted to- 

 gether, and projected towards the centre of the pit, requiring inside 

 cribs and planking in front, as, with the plank tubbing, the expense 

 and inconvenience of this plan, very soon brought into use crib upon 

 crib. 



Crib tubbing consisted of solid segments of oak or elm wood, 8 or 9 

 inches square, piled upon each other, the joints containing i inch deal, 

 wherein to effect a water-tight wedging. This species of tubbing was 

 much esteemed about the year 1806. 



Cast-iron tubbing, according to the present improvement, with flanches 

 projecting outward, and put together without screw-bolt, was first intro- 

 duced in the winning of Howdon Pit in the year 1804 — 5, and has con- 

 tinued ever since to be universally adopted. 



