Champlain Valley southward into the Valley of Vermont. The Vermont Lowlands are primarily underlain by sedimentary rocks, especially limestone and shale, though metamorphic rocks such as marble and slate are also present. Lake Champlain is situated in the Champlain Valley between the Green Mountains of Vermont and the Adirondack Mountains of New York, drained northward by the Richelieu River into the St. Lawrence River at Sorel-Tracy, Quebec (northeast of Montreal). Major tributaries of Lake Champlain include Otter Creek and the Winooski, Missisquoi, and Lamoille rivers in Vermont, and the Ausable, Chazy, Boquet, and Saranac rivers in New York. Lake Champlain also receives
Lake Champlain Seaway advancing beyond the early planning stages. The Great Depression cut the project's planning budget, while World War II and completion of the St. Lawrence Seaway delayed matters. The growth of road and air transportation reduced the need for a canal, but the project was still under serious consideration as late as 1962. As proposed, ships would have used a dredged channel in the Hudson River, transferred to an upgraded Champlain Canal, navigated Lake Champlain, traversed an upgraded Chambly Canal and St Ours Canal, and traveled a dredged route up the Richelieu River to Montreal. Today, the seaway's planned route is