. Physical and commercial geography; a study of certain controlling conditions of commerce. and Ravenna, originally on a lagoonlike Venice, is now 4 miles inland. Where deltas emerge as a resultof deposition or coast elevation they furnish arable land of extremefertility and ease of cultivation. Two thirds of the Mississippi delta(12,300 square miles, — 7,872,000 acres) is above water at its ordi-nary level and is growing seaward at the rate of one mile in sixteen 42 THE NATURAL ENVIRONMENT years. It is covered with plantations of sugar, rice, cotton, and cy-press excellent for lumber (fig. 6)
. Physical and commercial geography; a study of certain controlling conditions of commerce. and Ravenna, originally on a lagoonlike Venice, is now 4 miles inland. Where deltas emerge as a resultof deposition or coast elevation they furnish arable land of extremefertility and ease of cultivation. Two thirds of the Mississippi delta(12,300 square miles, — 7,872,000 acres) is above water at its ordi-nary level and is growing seaward at the rate of one mile in sixteen 42 THE NATURAL ENVIRONMENT years. It is covered with plantations of sugar, rice, cotton, and cy-press excellent for lumber (fig. 6). The delta of the Hwang-ho —Chinas sorrow—extends 400 miles along the coast and 300miles inland (see map, fig. 11). It is extremely fertile and denselypopulated (over 800 per square mile). The river which forms thisdelta is so changeable that it is useless for navigation, and its watersare restrained only by an elaborate system of dikes and canals ofgreat length. The first complete abandonment of its channel is sup-posed to have been in 2293 , the second in 602 Since then. Shang-bai Fig. II. Delta of the Hwang-ho the river has changed its course many times by reason of increasinglyfrequent floods and of the fact that less care has been taken to pre-vent them ; and we find disastrous overflows recorded in 1820, 1858,and 1887. During the last inundation many villages were destroyed,completely or temporarily, and the loss of life through drowning andfamine exceeded 1,200,000 people, considerably more than the entirepopulation of West Virginia, An illustration of the capriciousness of streams and of the difficultyof adapting deltas to the use of man is furnished by the ColoradoRiver (fig. 12). The lower part of this stream has few branches for TOPOGRAPHY 43 300 miles. The supply of silt from the canyons and mountains ofthe upper basin amounts at times, however, to over a million tons perday; at Yuma, from September, 1903, to August, 1904, 95,000,000tons were carried,
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