As has been said, the problem of digging the big ditch has been one of the transportation of the spoil, and this has involved numerous difficulties. In Culebra Cut no little difficulty was experienced in keeping open enough tracks to afford the necessary room for dirt trains. Slides came down and forced track after track out of alignment, burying some of them beyond the hope of usable recovery; often the very bottom of the cut itself heaved up under the stress of the heavy weight of faulty strata on the sides of the mountain; and sometimes the slides and breaks threatened entirely to shut up one end of the cut. In hauling away the spoil one improvement after another was made in the interest of efficiency. It was found at first that the capacity of a big Lidgerwood flat car was only about 16 cubic yards, and that with a sideboard on only one side of the car, the load did not center well on the car, thus placing an undue strain on the wheels on one side. The transportation department, therefore, extended the bed of the car further out over the wheels on the open side, and this served a triple purpose--it permitted the steam shovels to load the cars so that the load rested in the center, increased the capacity of each car by about 3 yards, and permitted the unloader plow to throw the spoil further from the track, thus adding to the efficiency of the dumping apparatus. Frequent breaks in the trains were caused by worn couplers. These accidents were almost entirely overcome by equipping each train with a sort of "bridle" which prevented the separation of the cars in the event of the parting of a defective coupler. In the operation of the unloader plows it was found that the big cables frequently broke when a plow would strike an obstruction on the car, and this caused no end of annoyance and frequent delays. Then someone thought of putting between the cable and the plow a link whose breaking point was lower than that of the cable. After that when a plow struck an obstruction the cable did not part--the link simply gave way, and another was always at hand. On the big spreaders no less than 51 improvements were made, each the answer of the engineers to some challenge from the stubborn material with which they had to contend. The major portion of the material excavated from the canal had to be hauled out and dumped where it was of no further use. From the Central Division alone, which includes Culebra Cut, upward of a hundred million cubic yards of material was hauled away and dumped as useless. At Tabernilla one dump contained nearly 17,000,000 cubic yards. A great deal of spoil, however, was used to excellent advantage. Wherever there was swampy ground contiguous to the permanent settlements it was covered over with material from the cut and brought up above the water level. Many hundreds of acres were thus converted from malaria-breeding grounds into high and dry lands.