Those of one and a half foot span are of a square form, and are constructed by laying down a foundation of concrete masonry, on which a course of well jointed stone, not less than nine inches thick is laid, forming a stone platform on which well dressed stone is laid, one or two courses high, for the abntments or side walls, and finished by a second course of well dressed flagging, not less than nine inches thick all the work laid in hydraulic mortar. ; The culverts over one and a half foot span, with the exception of three of twenty-five feet span, are constructed as follows :

A foundation of concrete masonry is formed, and in a few instances some timber and plank is used with it on this an inverted arch of well dressed stone is laid in regular ;

courses, to form the bottom channel of the culvert side walls or abutments are thence ;

raised to such height as required, the face being well dressed stone, laid up in courses, and backed with rough dressed work. An arch is then turned from the abutments, with well dressed stone in regular courses. Wing walls at the ends are constructed in different forms as circumstances required. The character of masonry in the large 25 feet culverts is similar to that above described, except they have no inverted arch. There are five road culverts of from 14 to 20 feet span, constructed of masonry of the same character. All the culverts are of stone laid in hydraulic cement. There are 33 ventilators constructed to give free circulation of air Ventilators. through the aqueduct. Eleven of them are constructed with doors that admit an easy entrance into the aqueduct. They rise 14 feet above the surface of the ground over the aqueduct, and are constructed with well dressed stone, circular in their form, slightly beveling or tapering towards the top, where the opening is 15 inches They are in diameter.