The concrete masonry was formed by mixing one part hydraulic cement, three parts clean sand, and three parts fine broken stone ; in some cases fine pebbles were in part substituted for broken stone. The masonry was all laid up in hydraulic cement, obtained mostly from the hydraulic lime of Ulster Co. The mortar for the stone work was composed of one measure of cement to three of clean sharp sand, and for the brick masonry and plastering, one of cement to two of sand. It may be proper to remark, that every cargo of cement was tested by actual experiment, after it was brought on the ground, before any was allowed to be used. This precaution has had a very salutary influence on the character of the work the cement in all cases ;

where it is exposed to view, in its exterior, or broken up for examination, or otherwise, has appeared highly satisfactory. In the commencement of the work, there was much difficulty in getting the workmen to lay their stone and brick in a thorough, full bed of mortar, which is obviously very important in hydraulic masonry. But a rigid system of inspection, requiring all imperfect work to be taken down and relaid, was successful in obtaining work of great compactness and solidity. The area of a cross-section of masonry in the aqueduct is :

Concrete masonry, - - 4.605 ) Stone in side walls, 21.572 V Do. inspandrils, - 2.690^28.867, Brick in arches and side facing, - - 13.658,