Note 174 — Chapter II
Reading edition
Of this irrigation some idea may be formed from an estimate that the Amazon drains an area of 2,500,000 square miles; that its mouth is 96 miles wide; and that it is navigable 2,200 miles from its mouth. Somerville's Physical Geography, vol. i. p. 423. Indeed, it is said in an essay on the Hydrography of South America (Journal of Geograph. Society, vol. ii. p. 250), that ‘with the exception of one short portage of three miles, water flows, and is for the most part navigable, between Buenos Ayres, in 35° south latitude, to the mouth of the Orinoco, in nearly 9° north.’ See also on this river-system, vol. v. p. 93, vol. x. p. 267. In regard to North America, Mr. Rogers (Geology of North America, p. 8, Brit. Assoc. for 1834) says, ‘the area drained by the Mississippi and all its tributaries is computed at 1,099,000 square miles.’ Compare Richardson's Arctic Expedition, vol. ii. p. 164.