Having thoroughly mingled the broken stone and mortar, the concrete is placed in its proper position and form, and brought into a compact state by using a pounder ; and is then suffered to remain until it set, or become indurated, before any work is commenced upon it. The object should be to mix as many stones or pebbles as will thoroughly bed in the mortar, allowing none of them to come in contact, but all to

be enveloped in mortar. This forms a body which becomes indurated and makes a foundation under the whole length of the Aqueduct like one continuous stone. It attains a degree

of hardness which gives it the appearance of the conglomerate bearing the name of Pudding-stone, and is an article of the greatest importance in forming foundations for walls of

great weight ; superseding in many instances, where the soil is soft, the use of piles or other timber foundation. Though we have evidence that concrete was used by the Ancient Romans in the foundations of some of their structures and even in the formation of their roads --such as the Appian-Way, and though we find it used in the foundations of the feudal castles of the Norman Barons of England, still it has not been introduced into the general practice of architure until quite a modern date, and even at the present time is not widely appreciated in this country as a material of so much importance in foundations. The side walls are laid up in a character of workmanship styled "rough-hammered work" the stone required to be of