It is probable the unfinished foundations will be completed, and the masonry raised above high water by the month of September, and several of the piers be carried up by the close of the season to their full height, ready to receive the arches." While these sheets are passing through the press, an examination of the whole line * of aqueduct has been made with most satisfactory, results ; the water was stopped off be-

MEMOIR OF THE tween the Croton and the receiving reservoirs, and a minute personal inspection was made by the chief engineer and his assistants, who passed through the whole conduit, and only, upon very close examination, were enabled to detect some slight defects, which a few days would suffice for repairing. The exterior of the work had suffered as little injury as could be expected from the frosts of winter, and the heavy rains of this spring and neither outside nor inside had anything occurred to interfere with the regular action, which the various structures were designed to accommodate and promote.

Among the enumerated causes of injury to the Roman aqueducts, it may be remembered, was the formation on the bottom and sides of the channel way, of a stony concretion,

produced by matter deposited by the water. It is therefore satisfactory to know, what indeed might a priori have been anticipated from the purity of the sources whence the

Croton is fed, and the granitic region through which it passes, that no such deposit is made by its waters. " A fine sediment," says Mr. Jervis, in a letter to the author of 22d April, " has been thickness is too deposited on the bottom and sides of the aqueduct, but as yet its depth or small to be measured with much accuracy. As near as I can estimate, it might reach one inch in thickness in thirty or forty years, if left so long undisturbed.