PROTECTION OF BANKS. 69 



give satisfactory results, both in permanence and in appearance, and a less hold for 

 the action of the water, and present no projections to damage craft. They are tight, 

 but where on a soft foundation a settlement of earth underneath and behind them often 

 occurs and causes a sinking, breaking their continuity, and not infrequently resulting 

 in serious consequences. This is particularly noticeable in masonry where mortar is 

 used. The solidification of the mass by the mortar permits a large area of earth under- 

 neath to give way before failure, and thus there may occur without warning a break 

 of considerable dimensions, and one which may be left unprotected, or be even unknown 

 during lengthened periods of high water. Where there is no' mortar in the joints the 

 paving will generally follow the sinking of the ground and keep it covered, and, if not 

 submerged, will at once reveal what is taking place. 



In order to reduce the quantity of stone required in a given area the pieces are 

 sometimes placed flat, in thin layers, which are held in place by vegetation. This 

 method has been used in France to a considerable extent. Usually flat stones are used 

 for this work, but along the Meuse " dog's-heads " (cobble-stones) are frequently employed. 

 The method generally consists in placing stones side by side on a graded bank, the joints 

 being filled with thin slips of willows. If the work is done at a favorable time the 

 willows at once take root and protect the stones by both branches and roots, the latter 

 at the same time penetrating the soil and thus forming a perfect connection between 

 the bank and its protection. These works are said to resist ice, the great enemy 

 to banks in many localities, better than the masonry protection above described. In 

 order to keep the willows in bush form and thus prevent the growth of obstructing 

 trunks it is necessary to cut them from time to time. It is claimed for this form of 

 revetment that it is at once an economical and efficacious mode of protection. 



Excellent results are obtained by using various forms of brush, poles, etc., in pro- 

 tecting banks in all countries. These materials are cheap and usually grow in profusion 

 near the points requiring works of defense. They are employed in a great variety of 

 forms but principally in the shape of fascines and mattresses. The former are bundles 

 of flexible branches held together by wires or other ties. They are placed close together, 

 either singly or in horizontal layers over the bank to be protected, to which they are 

 held by stakes driven into the soil. They may be woven into mattresses by means 

 of poles, and when so arranged they form an excellent and impervious covering of 

 great strength, and gradually become consolidated by deposit. 



The fascines used in Holland are 8 to 1 3 feet in length, and from i foot 4 inches to 

 i foot 8 inches in diameter. On the upper Rhine they are from 13 to 16 feet in length, 

 and from i foot 2 inches to i foot 10 inches in diameter. 



The mattresses are made in numerous forms and by several methods. They 

 consist essentially of poles, brush, branches, etc., woven together with wire, or fastened 

 with timber or ropes, sunk into position and held there by stone. In this country, of 

 late years galvanized iron and silicon bronze wire have been used for binding, ordinary 

 wires having soon rusted out and permitted the mattresses to go to pieces. Wooden 



