510 JUNCTION OF THE FRESH WATER OF RIVERS 



This anomaly is easily accounted for. Were the current of 

 the tide confined entirely to the channel of the river, an ar- 

 rangement of the waters, similar to that which existed in the 

 first experiments, would have prevailed. But during the flow- 

 ing of the tide, the sea-water soon occupies more than the 

 channel of the river, and spreads itself in various streams 

 among the hollows of the sand-banks. These streams reunite 

 at different places with the principal current, and, in this man- 

 ner, prevent the salt and fresh waters from gaining their natu- 

 ral relative position. But as soon as these sand-banks are co- 

 vered with water, the tide proceeds with regularity in its 

 course, so that the different layers of water can then arrange 

 themselves according to their specific gravities. 



A thousand grains of water obtained from the bottom, at the 

 height ofjlood, yielded by evaporation twenty-three grains of 

 salt, while the same quantity of water from the middle yielded 

 only eighteen grains ; and from the surface only seventeen 

 grains. This was a difference of no less than six grains, and 

 seemed to afford a decisive result. 



In order, however, to complete the series of observations, 

 I examined the conditions of the currents at half-ebb. The 

 same irregularities prevailed, as before observed at half-flood. 

 A thousand grains of the water, from the bottom, yielded after 

 evaporation eleven grains of salt ; from the middle, nine grains, 

 and from the surface, twelve grains. At this time the densest 

 water was at the surface, and the lightest occupied the middle. 

 The cause of this was obvious. Extensive portions of the 

 sand-banks had already been left dry by the receding tide, and 

 various currents of water, disjoined from the main stream by 

 the inequalities of these banks, were now re-uniting with it, 

 through various channels, and disturbing the natural arrange- 

 ment which had prevailed during the time of flood. 



Although 



