" x. A piece of stone engrafted into the rock, serving as a bridge to cross a chasm, opened by cutting down the top of the rock to that level, into the cave. Of this stone is formed a part of the border that encircles the work.
Figure 2 shows how the buttress, a, was terminated in the second course. It also shows the places of the trenails and wedges ; which in all these figures are shown in the same manner. The clotted lines everywhere refer to the course that is to come on ; and shows how it will break joint upon the course supposed laid.
"Figure :1 shows how the space n r K, in Figure 2, is filled up in Figure 3, being confined in by the rise of the step L at 11 r, and the cramps a b; the ground proving here irregularly shattered by cutting the steps for the former lighthouse.
"Figure 4 shows the structure of Course IN"., where, in this, as all the others, the stones lighter-coloured denote the Portland, the darker the moor-stone.
"Figure 5. The position of three joggle-holes, r, between this course and the nest above.
"Figure G shows Course VI. complete, which brings the whole work to a level with the reduced rock : it shows the joggle-holes for the eight cubes ; and the central plug-joggle, fixed in place at o, ready for the reception of the centre stone of Course VII.
"Plate IV.—Plans of all the different courses front the top of the rock to the top of the balcony-floor inclusive.
Figure 1. The proper plan of Course VII. relative to the section, Plate II. No. 2. As being the first entire course, the trenails and wedges are shown ; but afterwards omitted in the to prevent crowding the figures. The black lines and clotted lines show the joints of the alternate courses. The centre-stones, and the four stones surrounding, were alternately of the same size to the top of Course XIV.
"a. The centre plug, first set.
" b b. The square part of the centre stone ; from each of whose four sides a dovetail projects, and thereon are fixed the four stones c c, by joint-wedges and trenails, as per figure ; which five stones united make one stone, sufficiently large to receive eight smaller dovetail stones d d; and whose projecting parts form dovetails to receive another circle, or order of stones, fixed like the former. The cubic joggles are shown at e e.
"Figure 2. The plan of Course XIV. the funda mental solid, and on which the entry and well-hole are begun. It also shows the diminution from Course VII. Upon this figure is shown the distribution of the smaller cubic joggles, which take place upon the entire solid. The entry here
appears to have a small inclination with the E. and W. line, which was not noticed in the section, Plate H. No. 2, to avoid ambiguities.
"Figure 3. The plan of Course XV. being the first of the entry-door and well-courses.
"Figure 4. The plan of Course XVIII. showing the work of the entry closed in, and the solid re-united. Also the manner of hook jointing the four stones round the centre to each other ; which, in the courses below the entry-door, were united by dovetails to the centre-stone. Joint wedges were applied in the hook, as per figure. Thus the arrangement, in circles from the centre, was again complete. In the entry courses, as every piece had at least one cubic joggle and two trenails, the work was secure against all ordinary attacks of the sea : the weakness being on the east side ; but when capped and bonded together by this 1Sth Course, the whole was again considered as one entire stone, out of which the cavity had been cut.
"Figure 5 shows Course XXIII. ready for putting on the cap-course of the solid.
"Figure 6. The cap-course, making the store-room floor, in its finished state ; the first course of the habitable part of the building, viz. Course XXV. being upon it ; and show ing the store-room door, with its joggles, joint-stones, and cramps.
"The detached figure, relative to it, shows a part of the top of the wall of Course XXV. to a triple scale ; wherein in i i denote one of the pieces of stone, whereof sixteen complete the circle : f shows one of the joggles used in this part of the building; being slices of marble the size of a common brick, let half its thickness into the middle of the stone; so that the next course above, breaking joint upon the middle of this, according to the dotted line g g, half the joggle's length will take one of the upper stones, whose joint conies upon it, and the other half joggle the other : by which means every stone is fixed to its place, as it were, by two steady pins, one at each extreme. The black lines, h showing the joint at each end of this stone : the small lozenge figures, k and I, show the shape of grooves, cut from the top to the bottom of each end of each stone, and which, when two are joined together, form that figure : k denotes the lozenge empty, or unfilled, and 1 the lozenge filled with a joint stone.