The Thames below Woolwich, in place of flowing upon a solid bottom,
really flows upon the liquid bottom formed by the water of the sea.
At the flow of the tide, the fresh water is raised, as it were, in a
single mass by the salt water which flows in, and which ascends the
bed of the river, while the fresh water continues to flow towards the
sea.--_Mr. Stevenson, in Jameson’s Journal._