ATTACK AND DEFENCE. 167 



way, and here are erected the trench cavaliers, h ikw. To build these on 

 the scarp of the sap-ditch, q (Jig. 20), a gabion, b, is set and filled with earth, 

 then the ditch is widened for the parapet, one or two rows of gabions, c, are 

 placed, and upon these the gabions d, which are covered with fascines, and 

 thus the parapet carried still higher. The banquette is made with two or 

 three steps of fascines or sand-bags, k. After completion of the trench 

 cavaliers, hik (pi. 49, fig. 3), two saps are carried out, from o towards x, 

 16 to 24 feet from the crest of the covered- way, and the crowning of the 

 covered-way is constructed with the traverses b. While the breaching 

 batteries are here disposed and executed, the descent into the ditch is 

 begun, which goes, in dry ditches, to the bottom ; in wet, to the level of the 

 water. It may either be covered, and formed in steps, or covered and an 

 inclined plane, or open. When there is a good loamy soil, the first con- 

 struction is chosen (fig. 21) ; the angle of descent is determined according 

 to the horizontal distance, A b, from the point a, and the height of the coun- 

 terscarp-revetment, K, at A D, allowance being made for the horizontal 

 piece, D m, to the bottom of the ditch, and the number of steps is fixed. 

 Then, in the lodgment, Q, the slope, Q s, is excavated, so that when it 

 comes to the slope, X, it is three feet below the line A Z, and now begins 

 the excavation of the descent, which is made seven feet high, and five feet 

 wide. The commencement is made by setting up a frame, cgwg (fig. 22), 

 as soon as the excavation has been carried one foot. Then it is dug two 

 and a half feet further, and the second frame, h, set fourteen inches deeper. 

 The two are connected by laths, d. Then two-inch planks, y, are driven in 

 behind and over the frame, until the whole gallery is sheathed. The con- 

 struction is continued in this manner, forming the steps, cop, until the 

 point m is reached, whence the passage is horizontal ; the revetment wall, 

 K, is broken through and supported by stones. The descent after the 

 second manner is made open. For this purpose a blind (fig. 24) is used, 

 which consists of two side-pieces, x, and the transoms, y and z. In the 

 oblique excavation, which goes on constantly behind a traverse (fig. 23), 

 the earth is thrown to the sides; as soon as it has advanced about twelve 

 feet, the blinds (fig. 24) are placed, and over across these the roof beams, b 

 (fig. 25), which have notches at r?'. Upon these come three rows of fas- 

 cines, crossing each other, and then three feet of earth. The revetment- 

 wall being reached in one or the other manner, the passage of the ditch is 

 commenced, which for dry ditches is simple. In wet ditches a dike is con- 

 structed (fig. 23), by throwing in stone, D, and laying water-fascines, g ko, 

 secured by pickets of the breadth required, and two feet above the level of 

 the water. The completed portion of the dike is covered by a parapet of 

 gabions, sand- bags, and fascines, xRv z. If, instead of a dike, it is prefer- 

 red to construct a floating bridge (fig. 26, view, fig. 27, ground-plan), then 

 hurdles, a, of fascines are first laid to the breadth required ; crosswise upon 

 these, a second layer, g, and then the third hurdle layer, h. Upon these 

 come two beds of sleepers and stretchers, crossing each other, x y and wop, 

 the fields of which are filled up with brushwood, and upon this is laid a bed 

 of fascines, k. It is covered by a parapet, R V, as in the case just described. 



643 



