Plattsburg has the chief United States military post on the Canadian border, there being usually a large force stationed at the extensive barracks. It is also the terminus of railways coming from the Adirondacks, originally built to fetch out the iron-ores, of which it is an active market. One of these railways comes from Ausable Forks. Another is the Chateaugay Railroad, which has a circuitous route around the northern and eastern verges of the wilderness, from the Chateaugay and Chazy Lakes, where are the ore beds in a dismal region. Lyon Mountain, one of the chief ore producers, has its mines at two thousand feet elevation above the lake. Stretching far away to the northward is the immense Chateaugay forest and wilderness, extending into Canada. This railroad passes Dannemora, where is located the Clinton Prison, a New York State institution, at which it is said "they always have a number of people of leisure, who pass their time in meditation, making nails, cracking ore, and in other congenial pursuits." The railroad route cuts into the red sandstone gorge of the Saranac, and follows its valley out to Plattsburg. Some distance north of Plattsburg, and at the Canadian boundary, is Rouse's Point, a border customs station. This is the northern end of Lake Champlain, which discharges through the Richelieu or Sorel River into the St. Lawrence, the waters descending about one hundred feet, and mostly by the Chambly Rapids. The Chambly Canal, which locks down this descent, provides navigation facilities from Champlain to the St. Lawrence waters. ENTERING THE ADIRONDACKS.