Geologically, the Berkshires are bordered on the west by the Taconic Mountains, the marble valleys of the Hoosic River and Housatonic River and, further south, by the Hudson Highlands; to the east, they are bordered by the Metacomet Ridge geology. They are on the average lower and less prominent than the Green Mountains of Vermont, and form a broad, dissected plateau punctuated by hills and peaks and cut by river valleys. The Berkshires topography gradually diminishes in profile and elevation from west to east and from north to south, except where rivers have cut deep gorges and sharp bluff faces into the Berkshire plateau.