Within the boundaries thus roughly defined and the sea, lies a land said to contain a greater diversity of natural features than any other of equal area in the United States. To the west and north are the Berkshire Hills of Massachusetts, the Green Mountains of Vermont, the White Mountains of New Hampshire, and the scattered peaks of Maine. From a height of fifteen hundred to two thousand feet at the base of the mountains, a gently sloping upland descends gradually to Long Island Sound and the Atlantic. Although, at first glance, its surface seems to present only a confused mass of low-lying hills, their tops are seen to show a marked uniformity of level as they gradually slope downward toward the south and east; and geological evidence makes it almost certain that, at one time, this region was a plain, resulting from the wearing down, by denudation, of an earlier mountain range. Subsequent alterations in its surface, due to erosion and other factors, gave rise to the present uplands and lowlands, which have been of determining influence in the peopling of the section, the rugged uplands offering so hard a subsistence that they were nowhere willingly chosen for settlement so long as land might still be had in the lowlands. Although, largely in the eighteenth century, economic pressure in the happier valleys forced many farmers to move to the hills, the opening of the West drew many of them to the prairies during the following century, and the population, like water which had been forced above its level, slowly drained off the uplands again, through the sluiceway of the Mohawk Valley. To-day, dying hill-towns, abandoned farms, and the yet unpeopled wilderness of northern Maine, tell the story of this struggle against geographical conditions.[3] Footnote 3: W. M. Davis, _The Physical Geography of Southern New England_ (New York, 1896), pp. 26 _ff._