INLAND NAVIGATION.

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to about six times as much, deducting, however, one-third for what isalready done by nature.

“ Were the mounds to be constructed of the size and form abovementioned, I am persuaded hardly any one would doubt of their beingsufficient for the purpose intended by them, of confining the two rivers,and all the water that should come from the point of partition or headsource, with the other occasional streams that might fall into the channelin the course of the canal. But to convince the most incredulous, I shallgive an instance of a river above a thousand feet broad, navigable evenfor vessels of war, which is confined by artificial mounds, and whose sur-face is above ten feet higher than the adjoining ground on both sides.

" That river is the Thames, which in different places below London,particularly from the Ille of Dogs to the Woolwich-marffies, is fencedin on both sides by artificial mounds, though it be there above fifteenhundred feet broad, and the tide, during six hours of the four-and-twenty, be full ten feet above the surface of the adjoining ground.

" History, I believe, does not mention when these mounds were firstmade ; but probably without them there would be two hours less tideat London, and the navigation up and down would be more dangerous,as vessels might frequently be stranded on the shallow meadows : thus,though the Thames may justly be reckoned one of the first navigablerivers in Europe, it is nevertheless indebted in some degree for its navi-gation to art.

“ What has been done at the Thames is an example before our eyesof the easy practicability of what I propose for the present navigation.But besides the Thames, there are numbers of other rivers and artificialcanals carried above foil, without any inconvenience from soakage orleakage, or any danger to the banks themselves, which by their ownweight, and the moisture of the river, soon consolidate into one mass.

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