TRANSPORTATION OF THE DEBRIS 187 



contains shells, they are deposited in the chute. The shells create 

 around them deposits of sand which continually increase and must 

 be removed either with shovels, or by increasing the inclination 

 of the chute. A greater volume of water is of no avail. With 

 various degrees of fineness of the sand and mud, it was found that 

 different inclination of the chute were required. 



Mud behaves very much like sand. If it is sufficiently soft 

 to mix with water it will pass down a chute set with very 

 slight inclination. The very soft mud at Suez, such as that from 

 the old channels previously cut through the clay ground, does not 

 require the addition of any water in the chute. With clay it is 

 quite different; the addition of water washed away only a very 

 small quantity of the material, and hardly breaks up the lumps. 

 If each lump of clay were to slide perfectly straight down the chute, 

 all would work well; however, a lump winds about and soon stops, 

 and the contents of the next bucket drives it on 5 or 10 ft., and this 

 increases the trouble, until the mass gets to be 12 or 16 in. in thickness 

 and reaches to the top end of the chute, when the contents of the 

 succeeding buckets seem to break it up, and the mass descends 

 quietly and regularly in pieces of about 3 to 6 ft. length. The chutes 

 for clay are inclined from 1 in 12 to 1 in 16. With an inclination 

 of 1 in 20 the work is more regular. When the clay is mixed 

 with sand the surface acts like a rasp, because the water washing 

 away the clay leaves the grains of sand, and their grinding and 

 cutting are detrimental to the chute. 



Experience has thus shown that while a considerable supply 

 of water must be added to sand, it is not so for mud or clay, to which 

 just enough water must be added to moisten the mass. Jets of 

 water have not given good results; they merely wash down the 

 points against which they are directed and do not break up the 

 lumps. In dredges with chutes 230 ft. length an endless travel- 

 ing chain is employed, driven by the engine and furnished with 

 a series of scrapers to carry the clay down the chute. Generally 

 the greatest difficulty with all kinds of spoil is in passing through 

 the first 40 or 50 ft. of the chute. When once the material has passed 

 this with any given inclination, it continues moving on down the 

 same inclination without any further difficulty. 



Very often the materials removed from the bottom by hydraulic 

 dredges are used to fill up lowlands near by, and are transported 

 by means of a long line of pipes. The pipes used are of different 



