When unusual strength is required, the stones are not only united by laying in mortar or cement, but are further held by joggles, dowels, cramps, and bolts. Simple forms of joggle are shown in Figs. 1288, 1289, 1290, where a tenon a on one stone is fitted into a mortice b on the next. Fig. 1291 illustrates the operation of dowelling, in which the 2 stones a b are joined by the dowel c let into grooves cut in the face of the stones. Joining by cramps is shown in Fig. 1292, a b being the 2 stones as before, and c the iron cramp dropped into holes cut for its reception. The operation of securing railings in stone by leading is represented in Fig. 1293. When the upper surface of the stone carries the railings, the bar a stands in a dovetailed hole in the stone b, and is surrounded at foot by molten lead c poured in up to the top. But when the rail is to be fixed to the side of a stone, the bar d is bent so as to go to the end of the hole, and in order to fix it with the lead e, a bay of clay f is made to support the lead while it remains in a molten state, the clay being knocked away and the lead dressed flush when it is cold. Walls. - In building stone walls, the same care is needed with regard to breaking joint as in brick walls.

Footings should be done with the largest stones available, and the size may decrease with the rising courses; but all stones in one course should be of the same thickness. The arrangement of the stones in the courses will depend upon their shapes and sizes. Fig. 1294 illustrates an arrangement where the long stones a are equal to the full width of the wall, alternating with the short ones b. In Fig. 1295 the long stones a require the addition of the short ones b to make the full width. In Fig. 129G the long stones a are alternately used as headers and stretchers, the small ones b filling up the intervals. In Fig. 1297 there are no small stones, the spaces between the large ones a being filled with broken pieces or grouted rubble b. In "setting off" stone walls, there should not be a difference of more than 3 or 4 in. between succeeding courses.

Joining Stones 1145Joining Stones 1146Joining Stones 1147Joining Stones 1148

Enclosing walls of stone, if of no great height, are often built dry, i. e. without any mortar. There is frequently in stone walls a slope or " batter " on both sides amounting to 1 part of breadth of base to 6 of height, either carried gradually up or with offsets. Bubble walls have generally both sides vertical, the average thickness being 1/16 of the height. Superior walls are commonly provided with a coping at the top, to throw off the wet. This may have either a single slope to one side as in Fig. 1298, or to both sides as in Fig. 1299, the throating a in either case causing the water to drip away from the wall. Precisely the same plan is adopted with window sills.