Although the sand of Cape Cod is in some places three hundred feet deep, there is believed to be a backbone of diluvian rock. There is a clay vein, too, which slants across the Cape and crops out at Truro in the so-called Clay Pounds, now crowned by Highland Light, shining two hundred feet above the ocean. This hill of clay thus renders a sovereign service to that dangerous stretch of navigation. It must be borne in mind that Cape Cod runs out straight into the Atlantic for twoscore miles, by the south measurement, and then, [Illustration: HIGHLAND LIGHT.] abruptly turning, juts up another forty to the north. The shifty sand-bars of the Back Side have caught, twisted and broken the hulls of innumerable craft. One gale of wind wrecked eighteen vessels between Race Point, at the extremity of the Cape, and Highland Light. The average width of our crooked peninsula is six miles, but at Truro it narrows to half that distance. Across this strip the storms whirl the flinty sand, until the humblest cottage may boast of ground-glass window-panes. The coast outline is ever changing and the restless dunes show the fantastic carvings of the wind. The houses cuddle down into the wavy hollows, with driftwood stacked at their back doors for fuel, and with worn-out fishnets stretched about the chicken-yards. Here and there a pine-tree abandons all attempt at keeping up appearances and lies flat before the blast. The ploughed fields are as white with sand as so many squares of beach, and the sea-tang is strong in the air. Accustomed, before their harbor failed them, to depend chiefly upon the sea for subsistence, the people of Truro now find it no easy matter to wrest a living from what they have of land. Everything is turned to account, from turnips to [Illustration: OYSTER POINT, WELLFLEET.] mayflowers. Along those sand-pits of roads, bordered with thick beds of pink-belled bear-berries, or where the dwarfish pines, their wizened branches hung with gray tags of moss, yellow the knolls, are gathered large quantities of sweetest, pinkest arbutus for the Boston market.