In grand galleries the tenons at the top of the stanchions are usually shorter than the thickness of the cap-sill, and those at the bottom, as well as the mortises in the ground-sill, are omitted. The stanchions are kept from collapsing by blocks nailed to the ground-sills. These blocks are 2" thick, and wide enough (about 9´´) to so guide the wheels of a gun-carriage as to prevent the axle striking the stanchions. In cases for smaller galleries also the tenons are sometimes omitted at the bottom of the stanchions, the mortises in the ground-sills cut an inch or two deeper, and the stanchions kept from collapsing by keys driven in the mortises (Pl. XI, Fig. 13). =22. Shaft and Gallery Frames= (Pl. XI, Figs. 14, 15, and 16) are made of scantlings, halved together at the ends, as shown in the figures. _Sheeting_ is made of boards or planks of the necessary thickness, sawn to proper lengths, and bevelled at the ends. When sawn lumber is not available, the frames may be made of saplings, and in some cases poles may be used for sheeting. The middle of each cap and ground sill, both in frames and cases, is distinctly marked by a shallow saw cut or otherwise. =23.= The following table gives the dimensions, in inches, usually adopted for the pieces of cases, frames, and sheeting, for galleries of different sizes, viz.: ----------------+------------------------------------+--------------------------------------------- | Cases. | Frames and Sheeting. +------------+-----------+-----------+------------+-----------+---------+---------- |Ground-sill.|Stanchions.| Cap-sill. |Ground-sill.|Stanchions.|Cap-sill.|Sheeting. ----------------+------------+-----------+-----------+------------+-----------+---------+---------- | In. | In. | In. | In. | In. | In. | In. Great galleries | 3 | 4 | 5 | 6 × 4 | 6 × 6 | 6 × 9 | 2 Common galleries| 2 | 2 | 2 | 6 × 3 | 6 × 6 | 6 × 8 | 1½ Half galleries | 2 | 2 | 2 | 5 × 3 | 5 × 5 | 5 × 7 | 1½ Branches | 1½ or 2 | 1½ or 2 | 1½ or 2 | 4 × 3 | 4 × 4 | 4 × 5 | 1 or 1½ Small branches | 1 to 2 | 1 to 2 | 1 to 2 | 3 × 3 | 3 × 3 | 3 × 4 | 1 ----------------+------------+-----------+-----------+------------+-----------+---------+----------