New York lies upon the portion of the Appalachian Mountains where the mountains generally assume the character of hills and finally sink to a level of the lowlands that surround the great depression filled by Lake Ontario and the St. Lawrence River. Three distinct mountain masses can be identified in the state. The most easterly of these ranges—a continuation of the Blue Ridge Mountains of Virginia—enters the state from New Jersey and extends northeast through Rockland and Orange counties to the Hudson River, continuing on the east side of that river as the highlands of Putnam and Dutchess counties. A northerly extension of the same range passes into the Green Mountains of western Massachusetts and Vermont. This range is known in New York as the Hudson Highlands. The highest peaks are above sea level. The rocks that compose these mountains are principally primitive or igneous, and the mountains themselves are rough, rocky, precipitous, and unfit for cultivation.