Although all portions of the work were systematically pushed forward with a view to have them ready for their connections at the proper time, the principal effort was directed to the completion of the piers to the top of the granite skew-backs, so that the erection of the steel arches might be commenced as soon as the material was prepared.

While work was therefore actually begun under the plans of May, 1886, important changes in those plans were authorized, and changes, once commenced, did not cease until the completion of the bridge. Appreciating more fully as it progressed, the largeness of the work in their hands, the Commission decided that a higher class of constructive work and a more ornamented structure would amply justify the increased expenditure to the people of this great city, and all the changes were in the way of greater durability and beauty. The result has proved the correctness of their judgment.

MASONRY.

MATERIALS.

The granite used was from the quarries of Biddeford, Mt. Waldo, and Vinal Haven, all on the coast of Maine. As the latter has somewhat more color than that from Mt. Waldo, the effort was made to use them in different portions of the work, but this was soon found to be impracticable without delays. It is also undesirable for "rock-faced" or " quarryfaced" work.

The cornices, parapet, etc., were made from a finer quality of granite of uniform color, from the Mt. Waldo quarries.

The light gray gneiss ashlar for the long faces of the piers and facing the approaches, was from the Mine Hill quarries near Roxbury, Conn.

Rubble masonry was of gneiss from the vicinity, partly from a quarry on 7th Avenue, but largely from the excavations made for the foundations and for grading the adjacent ground.

The stone for concrete was chiefly supplied from limestone quarries on the Hudson River, which furnish large quantities to New York. It was crushed at the quarry by machinery, screened, and delivered by water at the site of the bridge.

The cement chiefly used on the work was Rosendale from the New

York and Rosendale Works. It was of excellent quality; tests for tensile strength of pure cement in twenty-four hours, ranging from 80 lbs. to the square inch to over 130 lbs., the average of over 2,000 tests being 96 lbs. tensile strain to the square inch. Small quantities of other cements were used, but the Rosendales are so well known and so cheap, that it was not thought well to try practical experiments with others. Nearly 40,000 barrels were used.

Portland cement, of which 24,000 barrels were used, was chiefly of the Hemmoor brand. It was finely ground and of excellent quality. Its strength under different conditions, is shown by the table of tests of cement. It was used chiefly where pressure might not be evenly distributed, whether from foundations of unequal hardness, or from pressure being applied at points, as under the skew-back courses, and generally in setting the face-stone.

The concrete was composed' of one part by measure of cement to two parts of sand and five of broken stone, no fragment of the latter being more than two and a half inches in any dimension. The concretemixer was a cast-iron box, 8 feet long, and 2 x 2 feet in transverse section, placed at a slight inclination and revolved on its longitudinal axis by a special steam-engine, while the dry material was admitted from a hopper into its upper end. Water was supplied by a pipe, and after several revolutions the concrete was discharged from the open lower extremity. Owing to frequent irregularities in the flow of the material, it was difficult to regulate the quantity of water; otherwise the mixing by this machine was fairly good, and was thoroughly completed by the successive handlings, before the concrete was in place in the work. The economy of mixing by machine over hand-mixing is very great. The capacity of this mixer was 150 cubic yards per day, requiring the services of twelve men. It was operated by a special steam-engine, at the rate of forty revolutions per minute. The concrete was carried from the mixer in iron buckets containing about a cubic yard. The buckets were lifted from the car by a derrick, lowered into the pit, dumped, and the concrete was spread and rammed,-care being taken that the concrete was level with the granite facing before another granite course was set,