When man first began the study of the earth's surface, he encountered at the very beginning, along the borders of the sea-coasts, on the lowland plains, and even on the hills, certain puzzling phenomena, difficult of explanation. These perplexing observations seemed to testify, by means of ancient raised beaches, fossil oyster and mussel shells, dessicated salt marshes, fragments of wrecks, and even by ancient anchors in the hills, that at some unknown time in the past the sea had “formerly been where the land now was.”