Chunks and fragments of clay are loosened by the weather from their beds in the cliffs and are often washed by heavy rains so that a gray liquid flows and fans out for some feet across the sands. Occasionally boulders will loosen and tumble down. In fact small stones are constantly falling, rolling erratically part way down the beach and leaving their tracks behind them. The cliffs are the prime source of the beach’s materials and a repository of the ages that preceded it. They have a proud and vulnerable role in a context where everything is subject to displacement and removal. Taking an average of three feet a year, the Outer Beach may have required 1760 years to erode a mile in width, even though that is one of those general figures which may mean nothing so far as detailed geological history is concerned. In any case, not only cottages and lighthouses have gone their way but also such topographical features as marshes and ponds, with all the frogs, fish, and plants that belonged to them. On the cliff tops and very close to the edge, there are many glacial kettle holes, now dried up, but once full of water instead of sand, so numerous in some areas as to make one uninterrupted dip and rise after another. On the Nauset Coast Guard Beach, where the cliffs have ended and are replaced by a long sandspit protecting the Nauset marshes behind it, there is good evidence, jutting out on the beach, of a former kettle hole, showing a fine dark sediment composed of organic material which once lay under beds of peat. The cliffs’ glacial material, in whatever form they were left on Cape Cod some 20,000 years ago, was part of the land’s erosion, of geology’s rising and falling history, for countless years before that. Since then it has been constantly exposed, loosened, easily eroded and ready for the taking, by winds, tides, and waves, but all of it was changing and movable in terms of the great stretches of earth time. Many of its stones and boulders were being wind and waterworn, cracked by frost and heat, long before they were plucked from hills and ledges, transported and left by the glacier to give the Cape its present form. Now they are being broken out and rolled down to be worn again. Like the tides, they are part of a balance, a flow, and containment, that is prodigious in its reach. The cliffs erode; the surf churns the sand; currents carry away the sand and other cliff debris; storms cause the sea to break in across sandspits and bars, so that they change constantly in shape and position. There is a magnitude of effect involved at this meeting place of sea and land. It is a magnitude that stretches between a sand grain which may be less than a millimeter in diameter to storms whose force makes man-made explosions of nuclear energy minuscule by comparison.