MERRIMAC  ,1 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 Ito 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 55 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 17a M. above its mouth, are the cities of Newburyport, near its mouth, and Haverhill, at the head of navigation .

In 1899-1908 the 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 .