Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/59

Rh one. Such beaches, however, do not travel, but gradually add to the surface of the land.

The following facts may also be appealed to in favour of the greater power of tidal currents:—a ship at anchor always rides with the tide, except in excessive wind; and then it is the wind, not the wind-wave, that veers round the ship. Fishermen's nets that break loose during a storm always float with the tidal current; so also do wrecks, timber, and the like: these being below or only a little above the surface of the water, cannot be driven by the wind; but if the wind-waves are more effective than the tidal currents, they ought to go with the former, not with the latter. We also find that off-shore banks and shoals always lie with the course of the flow-tide currents, irrespective of the direction of the most prevailing or most effective winds.

It will be found that if the effective winds come in a contrary direction to the flow tide, all permanent sand and gravel banks, diverting the "invers" or mouths of rivers and streams, are due to the currents of the flow tide. Continued winds in a contrary direction may often temporarily pile up a bank; but as soon as they cease, the bank is rapidly carried away and disappears. Many interesting facts may be learned from the study of wrecks on sea-beaches. If a ship is cast broadside on, and the wind and tidal currents are in the same direction, the beach inside the wreck is scooped out. If, however, the current and wind-waves are contrary, a bank is cast up behind the wreck, the greater accumulation of the sand being to