Mr. M. Dunn on the Sinking of Preston Grange Engine Pit. 231 



But to resume. — No sooner had the sinking reached the depth of 7 

 fathoms, than a feeder of water was met with of 200 gallons per minute, 

 and as it was found to deliver itself at the surface level, preparations 

 were made to dispose of it in the following manner. 



A ledge of water-tight Stone being made perfectly smooth and level, 

 the laying of the wedging crib (intended as the foundation of the tub) 

 was commenced, consisting of segments of oak timber, 9 inches broad 

 and 8 inches thick, every joint of which was lined with half-inch deal, 

 for the purpose of wedging. When properly adjusted, these cribs were 

 wedged both behind and at the joints as tight as possible, after which 

 the tub segments commenced building, each segment being 4 feet long, 

 2 feet high, and scarcely f inch thick, having flanches of 3 inches pro- 

 jecting outwards from each end and side of the segment, the space be- 

 tween each joint being also filled with slit deal like the wedging cribs. 



As the building of the tub proceeded, the joints being arranged off 

 and on, the space behind was closely packed with wood or stone, and 

 the top was surmounted with 8 feet of walling ; every joint was then 

 wedged so long as any leakage remained, when the water which had 

 before forsaken the neighbouring wells, returned, and discharged itself 

 at the surface. 



The sinking was then resumed without difficulty, till, at the depth of 

 22 fathoms from the surface, the shaft intersected the fissure of a trouble, 

 which gave out a new feeder of water, consisting of 300 gallons per minute, 

 and it was not until the pit had reached the depth of 28 fathoms, that 

 a suitable solid Stone could be selected whereon to found the wedging 

 cribs, for two were in this case judged prudent, and which were finished 

 after the manner before described.* 



The length of this tub was required to be 6| fathoms ; for, having 

 ascertained that this water also rose to the surface level, it became ne- 

 cessary either to join it to the upper tub, or to terminate it at some 

 intermediate water-tight rock, which latter mode was adopted as a sav- 

 ing of expense. 



When the necessary quantum of segments had been built, a pair of 



* See Plate IV. Fig. 2. 



VOL. II. 3 D 



