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.