direct, was for the Culebra Cut. There might be added to the total for the Culebra Cut $20,000,000 of the payment for the French property, which applied to excavation, thus indicating that the cut comprised over one-half of the construction work of the canal proper.

A typical American tool developed largely on railroad work, namely, the steam shovel, solved one of the vital parts of the excavation problem. Its function was to pick up the soft material or blasted hard material and place it aboard the cars. It performed its function so well that the rate of progress was dependent on keeping the shovels supplied with cars and disposing of the material on the dumps. Again allowing the cost of the various items into which excavation may be analyzed to indicate their relative importance, the following table, taken from the records for the fiscal year 1912, is given with the items arranged in the order of cost:

ANALYSIS OF COST OF EXCAVATING CULEBRA CUT, TAKEN FROM RECORDS FOR FISCAL YEAR 1912

The clearing of the site in preparation for excavation work was of minor importance. After the loose mate

rial had been cut away by the shovels, the drilling and blasting followed. Of the total of 93,000,000 cubic yards of material removed from the cut prior to July 1, 1912, about 66,500,000 cubic yards, or 71 per cent, required drilling and blasting. The power for drilling was supplied by a large compressed-air main, which was tapped at convenient points and the lines laid to the drills. The work was most carefully studied and planned. Systematic records were kept of the amount drilled by each crew daily. Familiarity with the material and trial of various methods indicated exactly the setting of the holes and the depths to which they should be drilled to obtain the greatest economy. All loading of holes and firing was placed in the charge of a special crew of trained men, and the firing was done by current from the electric station at Empire. There was a serious accident during the early stages of the work, due to a premature discharge of a vast quantity of dynamite that had been placed in the holes and left there for firing at a convenient time. From some obscure cause, such as the overheating of the dynamite, it exploded and killed a large number of men. Thereafter, the dynamite was fired within a few hours after being placed, with the result that in three years only eight men were killed by dynamite, although a total of 19,000,000 pounds of explosives was used in the Central Division during that time. A knowledge of the handling of explosives, as in the case of many other important public works, formed an asset of great importance. Various kinds of explosives were used, including saltpeter dynamite with 60 per cent nitro

glycerin, saltpeter dynamite with 40 per cent nitroglycerin and Trojan powder. The total amount of explosives used on the entire canal work to June 30, 1913, reached the enormous total of 56,000,000 pounds. When the blasting did not break up the material small enough for handling by steam shovel, it was further broken up by so-called "dobe" shots, which consisted in laying a small stick of dynamite on the top of the rock and detonating it with a safety fuse.

The shovels worked on short pieces of track, which were extended as the work progressed, while the cars for receiving the material were handled on parallel tracks next to the shovel. So rapidly did the shovels load cars that the handling of dirt trains into and out of the cut was a problem in railroad transportation of the very first order. Within the limits of the cut there were nine parallel tracks to carry the traffic, having a total length of over one hundred miles. Where two or more shovels were working on one line, the empties came in on one end of the track, so that each shovel had a train of cars. As soon as any shovel filled its train, all were immediately shoved ahead so as to get the full train out of the way. By adhering to this system the first train was always the one to be loaded first. All trains were handled by a train dispatcher and his assistants, who were located in a tower in a commanding position and provided with telephones, flags, and other forms of signalling apparatus. A great deal depended on the manner in which the train dispatcher handled his work. There were empties to get into the cut over a complicated system of tracks

FIG. 11.- Bird's-eye view of Pedro Miguel twin lock from Cerro Luisa, looking west. Upper waters are at Gatun Lake level. Lower waters are part of Miraflores Lake. Note emergency dams and five gates in each lock. Temporary bridge at right-hand end to be removed.