  Surprising as it may seem, there was a time when many of our most beautiful beaches, the Castle Neck area included, were far inland from the edge of the sea. This was about a million and a half years ago, when the sea was at a lower level than it is today. In fact, a great many changes have helped to form the beaches we see and enjoy now. Of them all, the one brought about by the Ice Age was probably the most influential. It was some 30,000 or 40,000 years ago that New England was overwhelmed by the final advance of a great continental ice sheet. It came from the northwest, and as it inched its way toward the ocean it pushed chunks of rock and great quantities of soil along with it. The rock was continually breaking up as it was shoved forward under the ice. This last glacier covered New England for thousands of years. When it melted, all the debris it had been moving along like a giant bulldozer was left deposited irregularly over the land, some debris perhaps a hundred miles from original location. In addition, the water from the melting ice swept finer sands and gravels along, depositing them over land areas and in lakes and bays. In some places, streamlined hills of debris had been built up under the ice. Later, as the ice melted, they became exposed. They were shaped like the bowl of an inverted spoon, and we call them “drumlins.” Hog Island, to the south of Castle Neck, is a perfectly preserved example. From its shape it is easy to tell which way the ice was moving. The steeply sloping end of its long axis is toward the northwest, the direction from which the last ice sheet came. All drumlins are not so easily spotted. About a mile southeast of Castle Hill you will see a hill that looks like an enormous sand dune. It is the highest point on the Neck, about eighty feet, and it, too, is a drumlin. Once it protruded out of a shallow bay that had formed as the ice melted. Modified by the erosion of the waves and veneered with windblown sand, this drumlin by now has quite lost its characteristic shape. In the general Boston area many drumlins were uncovered as the ice melted; some of them are such well-known landmarks as Beacon Hill, Bunker Hill, or Breed’s Hill. Along the coast, as the sea level rose, the drumlins there were surrounded by water and became islands. On the sides exposed to the sea they were eroded by the waves, and the eroded materials collected to form spits. Other sands and gravels carried by longshore currents were added, and, by-and-by, in some cases these sand spits connected one drumlin to another. It was just such a modification of three separate drumlins that formed Castle Neck. While the Neck was thus taking shape, the glacial debris and outwash sands that had been deposited in New Hampshire and at the mouth of the Merrimack River were being picked up and carried southward by the prevailing currents. Finally this material was wave-tossed onto the newly created beach at Castle Neck, some of it being lifted and carried farther inland. In this way, except for a few protected spots behind the drumlins, the entire area became blanketed with sand. The shape of the Beach as we see it is the result of this ever-continuing modification, the work of wind and waves. It was on the protected back side of the drumlins that plants first took hold. Since the drumlins were formed from fertile soil scraped from rich inland areas and carried here by the ice, the same kinds of plants sprang up on them—Aspens, Pines, Gray Birches, shrubs, and grasses—as we often see today taking over some abandoned farmland. As these early plants died, the soil was further enriched to stimulate even more and different plant life. In fact, at one time much of the dune area was a fertile spot, abounding with all sorts of plants and animals. In certain places on the Neck today, very fertile soil can be found just a few feet under the sand, evidence that here was once a rich farmland. The broad flat areas of sand on the Beach were very susceptible to the whims of the wind. Now and then, as the wind eroded the sand particles from one place, and blew them to another, it piled them up against the base of some beach plant. Collecting here, the sand began to form a gentle slope with a sharp drop-off downwind. Continuation of this action sometimes built up a huge mound, which we call a dune. This process of erosion and deposition still goes on. Usually you can tell the general direction of the prevailing wind by observing which way it builds the gentle slope as it piles the sand into ripples or mounds. If you should mark a dune’s position today and return in several years, you might find that the dune had moved several yards from its original position. Dunes move slowly downwind, such movement being termed “migration.” With a normal dune, during windy periods the sand is blown up its gentle slope and dropped over its crest, whence it slides down the lee side. In this way the dune migrates with the wind. THE FUTURE OF CASTLE NECKEventually, of course, the dunes might migrate the entire length of the Neck and again be blown into the sea, which would carry the sands farther south, mayhap to become part of Coffin and Wingaersheek Beaches. In fact, we might expect the eventual removal of the entire Neck if sand wasn’t constantly being added from similar erosion going on farther north. Obviously there is a very delicate balance here, adding and subtracting sand. The future of Castle Neck is entirely dependent upon the sand supply from the north. Too little may eventually diminish Crane’s Beach; while an increase could create GEOLOGICAL DISCOVERIES YOU CAN MAKEVentifactsThese small, faceted pebbles found in the dunes have been blasted by the windblown sand. They show the powerful abrasive action of the wind. Most of those you will find here were faceted just after they had been deposited by retreating glacial ice. A migrating dune or a blowout in the sand has left them uncovered. ErraticsLarge rocks occasionally found in the dunes are called “erratics.” In this world of tiny particles they appear very much out of place, but they were carried here by the glacier a million years ago. They have been uncovered by the migration of some dune. FulguritesOccasionally lightning strikes the sand, fusing it into a little tube or ball of glass. These fulgurites have been found here but are very rare and a real “discovery.” Glacial TillThe original soil deposited by the glacier may be seen by digging into the sand at the drumlin. Such rocky soil is quite surprising to people who think the beach is nothing but a big “sand pile.” GarnetsExamine a handful of sand. You will find that it consists of light-colored particles (mostly Quartz) and of black particles. Under a microscope many of these dark particles look like little gems. They are actually a deep red and are true Garnets. Large Garnets are used as gem stones, small ones for sandpaper—further proof of the abrasive ability of windblown sand. History in the SandIn your handful of sand you may find particles that are neither Quartz nor Garnet. Minerals such as Feldspar, Biotite, Mica, Magnetite, Hornblende, and others can be identified by the geologist and are a clue to the original type of rock over which the glacier moved. Beach PorcupinesThese are hard-packed balls of twigs and grasses. Loose vegetable matter is very light and may be blown along by the wind for many miles. As it goes it adds other vegetation to itself, until packed into a very tight, hard ball. It may also get its start in the water by being whirled into a tiny ball; and later it is thrown onto the beach, to begin rolling along. A most curious souvenir! MORE ABOUT THE DUNESThe face of the land is a storybook waiting to be read. The following books will help you piece together some of the story:
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