The sand drawn up by a suction dredge is valuable material for land building. In fact, a suction dredge is often used for the double purpose of excavating and filling in low land. Sometimes its only purpose is to fill in tide flats to above tide level. The material is discharged through a pipe line which may be over a mile in length. This pipe line is supported on a string of wooden or steel pontoons. The pipe sections are connected by means of heavy rubber sleeves so as to make the line flexible. This permits the dredge to move about and also allows of moving the discharge end about to distribute the sand properly. Unfortunately all dredging does not consist of sand and mud. Sometimes snags and matted roots are encountered which give trouble. For handling such material rotary cutters are used. The bow of the dredge is fitted with a hinged ladder about sixty to seventy feet long in which the cutter is mounted. The ladder also carries the suction pipe close to the cutter. The ladder is lowered to the bottom and the revolving cutter chops up the roots into pieces which are drawn up into the suction pipe. The size of the pieces that are sometimes sucked up is remarkable. The greater part of the area of the New Orleans Inner Harbor Navigation Canal was filled with stumps and matted cypress roots. The cutters tore up and cut these roots and stumps and the pieces were transported through a pipe line about 600 feet long. Stumps that were too large to be handled in this way were undercut and sunk below grade. Cutters are used also for loosening packed hard bottoms and some of them will dig into hard pan and even soft rock. A pressure of 100 to 150 pounds per square inch is maintained in a discharge pipe twenty to twenty-four inches in diameter, which is enough to carry along heavy bowlders dug up by the cutter. THE DEEPEST MINE SHAFT So far we have dealt only with surface conditions, but man has not been content to stay on the surface of this planet. True, we have scarcely begun to explore the crust of the earth. The deepest mine in the world is the Morro Velho in the province of Minas Geraes, Brazil. Here the earth has been penetrated to a depth of 6,426 feet in quest of gold. This is a depth of less than a mile and a quarter and it shrinks into insignificance when we reflect that we must go more than 3,000 times that distance to reach the center of the earth. However, we have made material progress in shaft-sinking in recent years, and it is quite likely that the lure of scientific research may prove even more powerful than that of gold and that some day we shall be induced to dig many miles into the crust of the earth just to learn something more about this globe that whirls us through space.