Section of Geology and Mineralogy: Sea Level

Abstract

Going back, in our imagination, to the early stages of civilization on this earth, we may find a man having established his home somewhere in the flat country just back of a gently-sloping sand beach. He must have done this for reasons which seemed good to him, and if we pursue our inquiry further, we would suggest that they may have been about as follows:(1) The flat fertile country of the lowlands would make it easier for him to grow the food he needed than if he cultivated the steeply-sloping hillsides farther inland.(2) He would be near an additional source of food supply, to be taken from the , sea.(3) He would have more ready means of communication with his like-minded fellows by means of water transportation. Our remote ancestor, then, has established his home on the coast and it is not long before he has learned from experience that if he lands his dugout on the beach when the water's edge is far U. 8. Coast and otodetic Survey, Washington D. 0. This paper, illustrated by lantern slides, wai presented at the meeting of th% Section on November a, 1947.out from his door and does not pull his canoe well up on the beach, it will probably float away within a matter of relatively few hours. Conversely, if he lands when the water's edge is in close to his door he will, if he wishes to set sail again when the water has receded, have to drag his boat a long way down the beach before it can be floated.This state of affairs is forced on his attention and he eventually notices that there is a somewhat rhythmic quality to the behavior of the water's edge with relation to the tree line back of the beach.He talks the matter over with his family and perhaps with some of his neighbors. They agree that there is a tendency toward a repetitive cycle in the events concerning the behavior of the water's edge. Someone, perhaps one of his greatgrandchildren, eventually tumbles to the fact that this cycle of events comes fairly close to repeating itself every time the moon goes through its changes from new moon to half woon, full moon, half moon and back to new moon again. Once this idea has dawned on these people and they seek to prove that it is a fact, the study of the tides has begun.As it is not within the scope of this discussion to trace the history of tidal in- TRAH84CTIONS of The New York Academv of Sci-Editor: ROY WALDO MINER.