From Classic Encyclopedia 1911
MERRIMAC,' a river in the north-eastern part of the United States, having its sources in the White Mountains of New Hampshire, and flowing south into Massachusetts, and thence east and north-east into the Atlantic Ocean. With its largest branch it has an extreme length of about 183 m. The Merrimac proper is formed at Franklin, New Hampshire, by the junction of the Pemigewasset and Winnepesaukee rivers. The former is the larger branch and rises in the White Mountains in Grafton county; the latter is the outlet of Lake Winnepesaukee. The valley of the Merrimac was formed before the glacial period and was filled with drift as the ice retreated; subsequently the high flood plain thus formed has been trenched, terraces have been formed, and at different places, where the new channel did not conform to the pre-glacial channel, the river has come upon buried ledges, relatively much more resistant than the drift below, and waterfalls have thus resulted. The river falls 269 ft. in a distance of IIo m. from Franklin to its mouth. The greater part of the total fall is at six points, and at each of four of these is a city which owes its importance in great measure to the water-power thus provided, Lowell and 1 The name is an Indian word said to mean "swift water." In popular usage the spelling "Merrimack" is used at places along the river above Haverhill.
Lawrence in Massachusetts, and Manchester and Concord in New Hampshire; at Lowell there is a fall of 30 ft. (Pawtucket Falls), and at Manchester there is a fall of S5 ft. (Amoskeag Falls). The region drained by the river is 4553 sq. m. in extent, and contains a number of lakes, which together with some artificial reservoirs serve as a storage system. On the navigable portion of the river, which extends 172 m. above its mouth, are the cities of Newburyport, near its mouth, and Haverhill, at the head of navigation. In1899-1908the Federal government dredged a channel from Newburyport to Haverhill (14.5 m.) 7 ft. deep and 150 ft. wide at mean low water; vessels having a draft of 12.5 ft. could then pass over the outer bar of Newburyport.