CAUSES OF FRESH WATERS TURNING SALT. 43 



operating throughout the course of countless ages. 



The turning of freshwater rivers and streams, during 

 periods of drought, into salt water, is a matter, explained, 

 as we conceive, upon the same principles. All these 

 streams run through extensive flat plains, upon which 

 the floods have already deposited a considerable season- 

 ing of salt the course of the stream naturally marks 

 the area of lowest level. Then, as long as there is 

 plenty of water, the solution of salts is too weak to 

 attract particular attention: but after a long drought, 

 when the waters become greatly reduced, the solution 

 becomes so strongly concentrated by evaporation, that 

 the remaining water may be as salt as the sea, or 

 even salter and thus the most disastrous consequences, 

 both to men and animals, have been frequently brought 

 about. 



The sufferings from thirst during " El gran Seco" to 

 which we have already alluded are, even now, terrible 

 to contemplate. 



So little rain fell, Mr. Darwin assures us, that the 

 vegetation was entirely destroyed " and the whole 

 country assumed the appearance of a dusty high road. 

 Very great numbers of birds and wild animals," in 

 addition to the domestic stock, " perished for want of 

 food and water." So great was their distress that, 

 Mr. Darwin says, a man told him " that the deer used 

 to come into his courtyard, to the well which he had 

 been obliged to dig to supply his own family with 

 water, and that the partridges had hardly strength to 

 fly away when pursued." Even on the banks of the 

 great river Parana terrible scenes were witnessed, "the 

 cattle, in herds of thousands" in an agony of thirst, 

 rushing down into the river, " and exhausted by hunger, 



