[122] And in addition to these arguments they adduce the facts that many great and deep bays and gulfs of vast seas have been dried up, and have become land, and have so turned out no insignificant addition to the adjacent country when sown and planted, and on that soil there is still left plenty of proof of such spots having formerly been sea, in the pebbles, and shells, and other things which are commonly washed up on the sea-shore being found in them.