1S65.] Man and Nature. 159 



effects of irrigation — a proceeding far more extensively and success- 

 fully adopted in Southern Europe, and generally around the shores 

 of the Mediterranean basin, than persons who have not visited those 

 countries can imagine. In Lombardy alone it is estimated by com- 

 petent authorities, that every day in summer there is an amount of 

 irrigation " diffusing over 550,000 hectares (1,360,000 acres), forty- 

 five millions of cubic metres (about ten thousand millions of gallons) 

 of water." As near as can be ascertained, the amount of water applied 

 to irrigated lands is scarcely anywhere less than the total precipitation 

 during the season of vegetable growth ; and in general it much ex- 

 ceeds that quantity. Spain offers examples on an equally large scale. 



The practice of irrigation to this extent very seriously interferes 

 with the quantity of water that would otherwise be conveyed by rivers 

 to the sea. Thus, in the case of the Po, the quantity of water with- 

 drawn is estimated to be equal to the whole water-contents of the Seine, 

 under average conditions. The works now in operation in Egypt are 

 estimated to remove one-fifth of the whole quantity of water carried 

 down by the Nile. The climatic result of this change is often shown 

 in the poisonous and malarious state of the air where irrigation is 

 prevalent. The cultivation of rice, which always requires much 

 water, is uniformly unhealthy. There is reason to believe that the 

 salts (chiefly sulphate of soda and common salt) sometimes now found 

 on sterile tracts, are the results of former irrigation; and that many 

 parts of North Africa, and of Northern and Western India, now 

 barren, were once exceedingly rich. This remark applies especially 

 to the valley of the Nile in Egypt and Nubia, and some parts of the 

 great African Desert. 



Eiver dykes confining the course of a stream within definite banks, 

 may be added to the means by which marsh lands are reduced to 

 ordinary soil. 



The drainage of the Val di Chiana, and the alterations effected in 

 the Maremme, or marsh lands of Tuscany, have produced results on 

 the physical geography of the adjacent country exceedingly remarkable 

 and interesting. The valley of Chiana intervenes between the courses 

 of the Arno and the Tiber ; and it has been supposed, that in former 

 times the waters of the Upper Arno may by it have flowed into the 

 Tiber. At present, its waters connect with the Arno. The result of 

 the engineering operations by which this has been effected, is the 

 reclaiming of about 450 square miles of pond, marsh, and sickly 

 swamp, and the improvement of the sanitary condition of the whole 

 district. The natural slope has been reversed, and the water-shed 

 removed thirty-five miles farther south, greatly increasing the Arno, 

 and diminishing or helping to diminish the floodings of that river. 

 On the other hand, the waters of the Tiber have been lowered. 



The Tuscan Maremrne are by no means exclusively marsh lands. 

 The term includes much high land and even mountain peaks, one of 

 which rises to the height of 6,280 feet. The coast, however, is low, 

 flat, and recently formed, and malaria is prevalent to a height of 

 nearly 1,000 feet. By a series of engineering operations, the low wet 

 lands have been gradually filled up ; and thus the mud, which would 



