When you leave the channel that elbows through the tidal marshes and then goes under the shore road, Route 6 A, through the valley ending at the Herring Run, you go from one living community to another. You leave the thousands of fiddler crabs tunneling through marshy ground, the fat, olive-colored little salt-water minnows, or mummichogs, darting through green clouds of muck in the warm pools left by the tide, and muskrats, kingfishers, herons, ducks, or gulls. Some are permanent residents, others are itinerants, but all are presently bound together in the tidal grounds. They feed off one another, being both producers and consumers of food, and so sustain the balance of all their lives together. Such communities are the principal study of the ecologists--the interrelationship of living things in their environment. The alewife migrates from sea to ponds through the inland vein, from crabs and shellfish to robins, and frogs beyond the tide. Its migration runs through several different life communities, of which it is not strictly a part, although its progeny, the fry, will be a part of the food chain all the way along, the prey of many different kinds of fish and birds, and eaters themselves of food the ponds provide. But the alewife’s migrant continuity is like the water itself that runs unceasingly down the valley, and ties all the life together that adjoins it. The stream, on the north side of the shore road, used to run up the center of the valley where there is still a ditch dividing once cultivated cranberry bogs, but the watercourse was long since diverted to the eastern side of the valley. It was in that direction I went one half-showery, half-sunny day for a further exploration, but first by way of the short, bordering range of hills before going down again. Hills and scoured valley were left by the most recent continental glacier as it melted back from the terminal moraine of Cape Cod perhaps some twelve thousand years ago. I climbed the steep slope on the west side of the valley, nearest the Herring Run. Below me the long, snaky turns of the run went down from its rocky top where the waters were churning white and spilling over. As I walked up and down the slopes and across the small ravines between them, I could hear voices receding down by the Herring Run; and then a woodchuck whipped a whistle and dove when I came up, its brown rump disappearing into a freshly dug hole, which had an arc of sandy yellow dirt piled outside. On the way there were wild cherry, viburnum, hawthorn, pitch pine, and juniper sparsely growing, and I passed a dipping stone wall that marked an old boundary line. I picked up a wing from the remains of a dead herring gull on the ground, put it before the light wind, and was struck with what broad strength it held the air. As I came toward that knob of a hill where the gulls congregated, they flocked away with a simultaneous rush of wings and went crying high toward the Bay. The hill was bald,