upon which an inverted arch of cut stone is laid forming the bottom of the water-way : side walls of stone are built and surmounted by an arch of stone. The span, or width of water way, of the culverts built, varies from 1^ foot to 25 feet. Those of li foot span have a square form for the

water-way, and are constructed by making a foundation of concrete, upon which a flooring of well dressed stone is laid forming the bottom of the water-way, and from this, side

walls are built and covered by a course of thick stone flagging well dressed and closely fitted. At each end of the culvert a deep wall is built underneath so as to prevent the water from doing injury by undermining it. Buttresses and wing walls are built at each end of the culvert to guide the water to and from the channel-way, and a parapet wall is

built over the top of the channel-way at each end to sustain the embankment of earth over the culvert. These wing walls and parapets have various forms ; sometimes the parapet is built across the top of the culvert, and the wing walls built at right angles to it, and sloping down to the but-

tresses, and sometimes the wing walls and parapet form one

continuous wall of a semi-circular form, the top sloping up from the buttresses in a plane parallel with the slope of the embankment covering the Aqueduct above. These culverts are permanently constructed, and in preparing the plans for them much skill has been displayed in adapting the form and size which the circumstances required, and much taste displayed in the design for their construction. Plate VII. is an isometrical drawing of one of the culverts with rectangular wings and parapets ; the body of the culvert is cut in two in the drawing, showing that it may be of any length, according to the width of the embankment through which it is The length is generally constructed. arranged so that the slope of the embankment may intersect the rear of the top of the parapet and pursue a direction down, parallel with the slope of the top of the wing walls.