Page:Cape Cod (1865) Thoreau.djvu/114

100 rid of. Sponges, which are picked up on the shore, as is well known, retain some of the sand of the beach to the latest day, in spite of every effort to extract it.

I found one stone on the top of the bank, of a dark gray color, shaped exactly like a giant clam (Mactra solidissima), and of the same size; and, what was more remarkable, one half of the outside had shelled off and lay near it, of the same form and depth with one of the valves of this clam, while the other half was loose, leaving a solid core of a darker color within it. I afterward saw a stone resembling a razor clam, but it was a solid one. It appeared as if the stone, in the process of formation, had filled the mould which a clam-shell furnished; or the same law that shaped the clam had made a clam of stone. Dead clams, with shells full of sand, are called sand clams. There were many of the large clam-shells filled with sand; and sometimes one valve was separately filled exactly even, as if it had been heaped and then scraped. Even among the many small stones on the top of the bank, I found one arrow-head.

Beside the giant clam and barnacles, we found on the shore a small clam (Mesodesma arctata), which I dug with my hands in numbers on the bars, and which is sometimes eaten by the inhabitants, in the absence of the Mya arenaria, on this side. Most of their empty shells had been perforated by some foe.—Also, the

Astarte castanea.

The Edible Mussel (Mytilus edulis) on the few rocks, and washed up in curious bunches of forty or fifty, held together by its rope-like byssus.

The Scollop Shell (Pecten concentricus), used for card-racks and pin-cushions.

Cockles, or Cuckoos (Natica heros), and their