These high tides of enormously distant past ages constitute the denuding agent which the geologist required.
So far we have dealt mainly with the earth and its moon; but is the existence of tides limited to these bodies?
Who would ever have imagined, under this terrestrial crust, an ocean with ebbing and flowing tides, with winds and storms?"
If either rotate on its axis, in the same or nearly the same plane as it revolves, that one is necessarily subject to tides.
In Celtic folk tales high tides and valley floods are accounted for by the presence of a "great beast" in sea, loch, or river.
But the constant motion of the tides offers, at some favored points, a source of power that will remain as long as the earth revolves upon its axis.
The energy of the tides is, in fact, continually being dissipated by friction, and all the energy so dissipated is taken from the rotation of the earth.