=33.= When the soil is very bad a _shield_ (Pl. XII, Fig. 20) is used to prevent the earth in front and above from caving into the gallery. In starting out from the shaft the following method is adopted: As soon as the top sheeting is sufficiently advanced and the shaft sheeting is forced down about 1 foot, the top plank of the side sheeting is inserted and driven forward about 2 feet, and the earth at the top of the gallery is excavated for from 6 inches to 1 foot in advance. A piece of plank a foot wide and in length equal to the width of the gallery is then placed directly under the top sheeting and against the face of the excavation, and is held in place by braces at its ends secured to the shaft lining. The shaft sheeting is then lowered another foot, the next plank of the side sheeting inserted, the earth excavated, and a second plank of the shield placed in the same way as before. This is continued until the entire face is covered. The top and side sheeting are then driven forward, and the top plank of the shield is removed and replaced in advance; after which each plank is removed and replaced in succession, as above described. =34. Inclined Galleries.=--_Method of fixing the slope._--If the gallery instead of being horizontal is _ascending_ (Pl. XII, Fig. 21) or _descending_ (Fig. 22), the proper slope is obtained by using a _slope-block_ whose edge is equal to the rise or fall of the gallery in one interval. This is placed upon the lower of two consecutive ground-sills, and the proper height of the other is determined by a mason’s or spirit level (Fig. 21). If a field-level or a mason’s level properly marked for the slope is used, the slope-block may be dispensed with (Fig. 22). =35. Position of Frames.=--In driving _descending galleries_ better progress will be made and less material used if the frames are set at right angles to the axis of the gallery (Pl. XII, Fig. 22); and this is the usual custom. In driving _ascending galleries_ this is impracticable, and the frames are set vertically (Fig. 21). In all other respects inclined galleries are driven in the same manner as horizontal ones. =36. Partly-lined Galleries.=--In very firm soil side sheeting may be omitted entirely, and in that less firm the side planks need not be in contact. When the side sheeting is omitted the width of excavation may be reduced to the clear width of the gallery, and the stanchions be let into the side wall flush with its surface. In this case the ground-sills are frequently omitted, the stanchions resting upon wooden blocks, stones,or directly upon the earth. To save material, the planks of the top sheeting are sometimes more or less separated also. This can only be recommended when rapid and temporary work is required with limited materials; and in these cases the earth between the planks should be supported by a packing of sticks, brush, etc., etc.