for. It was open at both ends to allow wagons to be driven in and emptied by dump boards, and at the end next the bridge a platform was built overhanging the declivity to make a turning place for the empty gravel and water wagons. During the middle of the day a high wind was generally blowing through the canyon, and to avoid the necessity of work at this time, concreting was begun as soon after daylight as possible with all available force, continuing all day if conditions were favorable, but quitting with the completion of a predetermined amount if the wind came up too strong. In this way each pier and arch were made monoliths. Owing to the cramped space, to prevent interference with the gravel carts supplying the mixing boards, it was found best to run the gravel wagons in the afternoon and evening after the concreting for the day was done. The water wagon was also kept running at the same time, filling all the barrels there was room for, and running next day during the concreting if necessary, which was usually the case.

Two handcarts, each of half a cubic yard capacity, were used to move the sand and gravel from bin to mixing boards. The proportions of sand and gravel were regulated at the bin, a foreman being in constant charge. One, two, or three mixing boards 8 by 12 feet were used, as many as space permitted; six men to each board in shifts of three. The mixture was turned by shovels once dry, three times wet, then shoveled into the forming, and spread and tamped in 6-inch layers by as many tampers as could conveniently work in the inclosure. In filling in the bottoms of the deep piers the concrete was put in and tamped in layers of 14 feet thickness; with a drop of 25 to 40 feet, together with the wet mixture employed, it was thought this would suffice. Most of the concrete was put in so wet as to quake after being tamped a minute or so; the arches were put in drier. The material was mixed in batches of six-tenths cubic yard per batch. The narrow space would not allow larger boards. In concreting the arches the haunches were first filled in 12 inches and the crown 4 inches, then the wire netting was put in place and the arch and rail completed.

Some of the difficulties encountered in this work are as follows:

1. Owing to the high wind usually prevailing the work of concreting was carried on under the most trying conditions, dust and cement filling eyes and lungs of workmen in spite of goggles and kerchiefs. On this account men kept constantly quitting, notwithstanding increased pay for concrete work, their places being filled by new and inexperienced men. Of the original force which began the work few were working at its completion, although a nearly uniform number was maintained by new recruits. The total number of men employed in connection with the work was 91, but the average force available was much less than this. The actual time spent by the force in concreting was 122 hours on 19 different days.

2. Owing to the complicated shape of the forming on the face of the cliff the cost of its erection was more than ordinary. It must be remembered, however, that this item includes tearing down the old bridge.

3. Lack of storing space near at hand increased the cost of handling all materials. 4. Labor and subsistence are probably as high here as in any part of the United States. Ordinary labor is paid for at $1.50 per day, of eight hours, and subsistence. This latter costs about 35 cents per day per man. All laborers while making concrete received 25 cents per hour.

5. Transportation rates are high. The rate from Cinnabar, the railroad terminus, to the Golden Gate, a distance of over 11 miles, is 283 cents per ton-mile.

6. A suitable sand and gravel for concrete is difficult to obtain. Of the money spent for this material, half was spent in exploring and stripping before it was made accessible.

On this last point developed an interesting question. What percentage of loam in sand will materially affect the strength of concrete? In the piers some material was used which contained 7 per cent (by volume, or less than per cent by weight) of loam. Better material could have been obtained only at greatly increased cost. In the arches no material used contained over 2 per cent of loam. The percentages were obtained by washing samples in a bucket of water, pouring off and evaporating the matter in suspension while thoroughly agitated.

The only information I have been able to find on this point are the experiments made by Mr. E. C. Clarke. In Mr. Clarke's test, sand containing 10 per cent of loam was used in the place of clean sand. Although his tests were not very decisive they indicated that for one week and one month the breaking loads are not much more than one-half what would have been expected with clean sand, but for six months and a year they are fully equal to ordinary mortar. These tests were made with Rosendale cement.

In some other tests conducted by the same authority clay was substituted for loam and Portland cement used, and the results obtained from breaking about 350 briquets