east line of St. Lawrence County. It is a broad, deep river, flowing with a strong yet sluggish current until it passes the limits of this state. In the upper part of its course it encloses a great number of small islands, known as the Thousand Islands. The surfaces of the Great Lakes are subject to variations of level, probably due to prevailing winds, unequal amounts of rain, and evaporation. The greatest difference known in Lake Erie is , and in Lake Ontario . The time of these variations is irregular, and the interval between the extremes often extends through several years. A sudden rise and fall of several feet has been noticed upon Lake Ontario at rare intervals, produced by some unknown cause. State parks New York has many state parks and two major forest preserves. The Adirondack Park, roughly the size of the state of Vermont and the largest state park in the United States, was established in 1892 and given state constitutional protection in 1894. The thinking that led to the creation of the park first appeared in George Perkins Marsh's Man and Nature, published in 1864. Marsh argued that deforestation could lead to desertification; referring to the clearing of once-lush lands surrounding the Mediterranean, he asserted "the operation of causes set in action by man has brought the face of the earth to a desolation almost as complete as that of the moon." The Catskill Park was protected in legislation passed in 1885, which declared that its land was to be conserved and never put up for sale or lease. Consisting of of land, the park is a habitat for bobcats, minks and fishers with some 400 black bears living in the region. The state operates numerous campgrounds, and maintains over of multi-use trails. See also Appalachia Glacial Lake Albany References External links