" It is obvious that there was no necessity for making moulds for a whole course after the work became regular ; as was the seventh course, after the six foundation courses brought the rock to a level ; it was sufficient to make one mould to each circle of stones, beginning with the centre stone ; but as the six foundation courses were adapted to the particular irregularities of the rock, and consequently could not be strictly regular, it was necessary that a separate mould should be made for every separate stone composing that part of the work.
" During this interval, I visited the rock, and on arriving there the 8th of September, was informed by Mr. Jessop, that the preceding evening, there being a very strong tide, and no wind, a \Vest-Indianian, homeward bound, and a man-of-war's tender, were in great danger of driving upon the north-east rock ; but that he timely perceiving their danger, though they themselves were. not aware of it, ordered out the seamen and hand; who towed them off.
"On this visit, I staid two days; for as the working com pany had begun to take down the upper part of the rod:, it was necessary to concert, and put in practice, the proper means of doing that, without damage to what was destined to remain. I have already mentioned my resolution of not using gunpowder ; yet it was necessary, for the sake of dis patch, to employ some means more expeditious than the slow way of crumbling oil' the matter by the blunt points of picks. It has been already noticed, that the laminae com posing the rock were parallel to the inclined surthee ; and it was very probable that the chasm into which Mr. Winstan ley's chain had been so fast jambed, that it never could be disengaged. extended thrther into the rock than the visible disunion of the parts : this made me resolve to try a method sometimes used in this country, for the division of hard stones, called the key and feather, in order to cross-cut this upper stratum of the rock. The construction and operation of the key and feather is as follows:—A right line is marked upon the surface of the rock or stone to be cut, in the direc tion in which it is intended to be divided. Holes arc then drilled by a jumper, at the distance of six or eight inches, and about one inch and a quarter in diameter, to the depth of about eight or nine inches; the distances, however, of the holes, and their diameters, as well as their depth, are to be greater or less, according to the strength of the stone, in the estimation of the artist directing the work. The above
dimensions were what we used on this occasion. The key is a long tapering wedge, of somewhat less breadth than the diameter of the holes, and so as to go easily into them; the length being three or four inches more than the depth of the holes. The feathers are pieces of iron, also of a wedge-like shape; the side to be applied to the key being flat, but the other side a segment of a circle, answerable to that of the holes; so that the two flat sides of two feathers being applied to the two flat sides of the key, and the thick end of the feathers to the thin end of the key, they all together compose a cylindric, or rather oval kind of body ; which in this position of parts is too big to go into the holes by at least one-eighth of an inch; that is, in the direction of a diameter passing through the three parts; but, in the other direction, is no broader than to go with ease into the holes. A key and a pair of feathers is made use of in each hole ; and the feathers being first dropped in, with the thick ends downward, the keys are then entered between them ; the flat sides of all the keys and the feathers being set parallel to that line in which the holes are disposed ; the keys are then driven by a sledge-hammer, proceeding from one to another, and being forced gradually, as in splitting of moor-stone, the strongest stones are unable to resist their joint dint ; and the stone is split according to the direction of the original line, as effectually, and much more regularly and certainly, than could be done with gunpowder, and without any concussion of the parts. Ilad our rock been entirely solid, this way of working might not have been applicable, on account of the crack's going too deep; but here, when it arrived at the joint where the chain was lodged, the split part became entirely disengaged from the rest ; and in this way we were enabled to bring off the quantity of several cubic feet at a time: and thus the chain was released. after a confinement of above fifty years. The impossibility of disengaging it before now appeared very evident ; for the pressure had been so great by the rock's closing upon it, as before suggested, that the links in their intersections were pressed into each other, as completely as it they had been made of lead; though the bolt-iron composing thee hair had been at least five-eighths of an inch in diameter.