Note 245 — Chapter XIII
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“The distances to which river water, more or less charged with detritus, would flow over sea-water, will depend upon a variety of obvious circumstances. Captain Sabine found discoloured water, supposed to be that of the Amazons, three hundred miles distant in the ocean from the embouchure of that river. It was about 126 feet deep. Its specific gravity was = 1·0204, and the specific gravity of the sea-water = 1·0262. This appears to be the greatest distance from land at which river water has been detected on the surface of the ocean. If rivers, containing mechanically suspended detritus, flowed over sea-water in lines which, in general terms, might be called straight, the deposit of transported matter which they carried out would also be in straight lines. If, however, they be turned aside by an ocean current, as was the case with that observed by Captain Sabine, the detritus would be thrown, and cover an area corresponding in a great degree with the sweep which the river has been compelled to make out of the course, that its impulse, when discharged from its embouchure, might lead it to take: supposing the velocity with which this river-water was moving has been correctly estimated at about three miles per hour, it is not a little curious to consider that the agitation and resistance of its particles should be sufficient to keep finely comminuted solid matter mechanically suspended, so that it would not be disposed freely to part with it, except at its junction with the sea-water over which it flows, and where, from friction, it is sufficiently retarded. So that a river, if it can preserve a given amount of velocity flowing over the sea, may deposit no very large amount of mechanically suspended detritus in its course from the embouchure, where it is ultimately stopped. Still, however, though the deposit may not be so abundant as at first sight would appear probable, the constant accumulation of matter, however inconsiderable at any given time, must produce an appreciable effect during the lapse of ages.”—Sir Henry De la Beche’s Geological Researches, p. 72.