In contrast, it may be noted that the St. Lawrence River but slightly varies its flow, above Montreal, because of the restraining power of the Great Lakes, its feeders. The upper Mississippi rises not to excess because of the thousands of lakes and lakelets in Wisconsin, Minnesota, and Dakota, its sources. The floods occur in its southern portion, chiefly below St. Louis. But for this reservoir system its navigation in the upper portion would be seriously impeded in summer seasons. Disastrous floods can scarcely occur on the St. John's, St. Croix, Penobscot, Kennebec, Androscoggin, Saco, Piscataqua, Merrimack, Connecticut, or Hudson Rivers, except from damming of the ice in winter or springtime (and that cause is of rare occurrence), such is the elaborate system of reservoirs about the headwaters of these streams. This northern country is greatly benefited by these excavations occurring from geological causes. The Merrimack River has a water-shed of about four thousand square miles miles--one fiftieth part of that of the Ohio. It has the Winnipiseogee, Squam, and Newfound Lakes, and hundreds of ponds to fill, that store a large amount of water, before any considerable rise can take place in the river, and then they restrain the flow. No excess of water comes through the Winnipiseogee River, though it is the outlet of a water-shed nearly as great as of the Pemigewasset. The freshets of the Merrimack come chiefly from the last-named stream and minor tributaries. Without these reservoirs, the manufacturing establishments at Lawrence, Lowell, and Manchester, would cease to be operated by water-power during the summer droughts. The highest flow of water in the Merrimack known in forty-six years, as measured at the Lowell dam, was thirteen and seven-twelfths feet. This occurred in 1852. Only a few times have freshets exceeded ten feet rise over that dam. The greatest fall of water and rise of the freshet, in this valley, known at Concord, New Hampshire, occurred in August, 1826. This storm notably caused the land-slide in the Saco valley, which buried the Willey family. The next was in early October, 1869, which caused the slide of seventy-five acres of land on the western side of Tri-Pyramid Mountain into Mad River, in Waterville.