The beating, or comminution of the rock, was usually effected at Passy at the rate of from fifteen strokes to twenty strokes a minute. The rate of descent, of course, differed in a marked manner, according to the nature of the rock operated upon; but, generally speaking, the trepan was worked for the space of about eight hours at a time, after which it was withdrawn, and the shell let down in order to remove the _débris_. The average number of men employed in the gang, besides the foreman, or the superintendent of the well, was about fourteen: they consisted of a smith and hammerman, whose duty it was to keep the tools in order; and two shifts of men entrusted with the excavation, namely, an engine-driver and stoker, a chief workman, or sub-foreman, and three assistants. The total time employed in sinking the shafts executed upon this system in the North of France, where it has been applied without meeting with the accidents encountered in the Passy well, was found to be susceptible of being divided in the following manner: from 25 per cent. to 56 per cent. was employed in manoeuvring the trepan; from 11 per cent. to 14-1/2 per cent. in raising and lowering the tools; from 19 per cent. to 21 per cent. in removing the materials detached from the rocks, and cleaning out the bottom of the excavation; and from 8 per cent. to 10-1/2 per cent. was lost, owing to the stoppage of the engines, or to the accidents from broken tools, or to other causes always attending these operations. In the well of Passy there was, of course, a considerable difference in the proportions of the time employed in the various details of the work; and the long period occupied in obviating the effects of the slips which took place in the clays, both in the basement beds of the Paris basin and in the subcretaceous strata, would render any comparison derived from that well of little value; but it would appear that, until the great accident occurred, the various operations went on precisely as Kind had calculated upon. KIND-CHAUDRON SYSTEM. [Illustration: Section through Kind-Chaudron Well at Durham. Fig. 110.] In the year 1872 Emerson Bainbridge, C.E., drew attention to the Kind-Chaudron system of sinking mine shafts through water-bearing strata, without the use of pumping machinery, in a paper read before the Institute of Civil Engineers. As the operation is almost identical with that which would have to be carried through in the case of a well sunk through an upper series of water-bearing strata, of minor importance or of impure quality, past rock and into the lower water strata, as for instance through tertiaries and chalk into the lower greensand, the following extract from Bainbridge's paper may be read with interest.