The Cape is a narrow peninsula, a little terminal arm jutting out in to the Atlantic, constructed of loose material left by the last glacier some 20,000 years ago. Its upper part, starting beyond High Head at Truro and forming the Provincetown hook, or hood, is of recent origin. It lacks the cliffs that stand over the beach from a mile or so north of Highland Light to as far as the Nauset Coast Guard Beach at Eastham, and for the most part has a history of deposition and accretion rather than removal. It was formed by storms, tides, and currents, piling in sand and other materials from the shore to the south, over bars and reefs of glacial debris. The sand is still packing up around Race Point, as it is also adding to the shore south of Nauset to the tip end of Monomoy Island, while storms take it away from other parts of the shore line. Within living memory a large island called Billinsgate, on which there was a lighthouse and at one time a “Try Yard” for whales, disappeared under the surface of Cape Cod Bay. It now appears as a shoal at low tide and is otherwise covered over by water, although the rocky lighthouse foundations still show above the surface in all but the highest tides. On the Bay side the shore line has been filled in in some areas, while it has receded in others, revealing for example, the bones of horses and cows in the bank at the head of a beach, which were once presumably, some distance behind it. Many a cottage owner after a storm has found his living-room floor with nothing below it but the tide. Over the centuries great changes have occurred in the nature and extent of marshlands, inlets, ponds, estuaries, and beaches. No year, or even month, goes by without some alteration in the shore line. These changes, not always obvious, sometimes violent and immediate, are not such as to threaten the physical existence of Cape Cod for many thousands of years to come, but they are of the kind that accentuate its close relationship to water and tides and weather. As the map makers are well aware, it is not a static piece of land. It moves. The trunk of the Cape starts out from the mainland and then that slender curving arm juts up and out into the water with a kind of brave assertion beyond the continental limits; but it is the shape and sweep of waves and sands, of molding and at the same time of pulling away that strikes you most about it, as if it were a conception to be made or discarded, standing out in its trial. The whole physical earth, in spite of its apparent constancies, its orbital speed, the speed of light, the regularity of the tides, the fine, exact balances to life, is subject to rhythmic change, or in a deeper sense, to re-creation.