ORGANIC REMAINS IN RIVER DEPOSITS 593 



in semi-arid regions violent floods arise abruptly, sweeping down 

 the previously almost dry river beds, and converting them in a 

 few minutes into raging torrents, it is apparent that organisms may 

 be surprised and suddenly overwhelmed and their remains entombed 

 in the resulting deposits of the flood. We need only recall such 

 disasters as that which recently befell a transcontinental railroad 

 where the sudden flooding of a previously dry wadi swept away 

 a trestle and its load of cars, these with their luckless passengers 

 being buried in the sand and silt of the lower course of the stream. 

 The many unrecorded entombments of cattle and other creatures 

 by just such sudden floods would, if known, form adequate illus- 

 trations of the origin of many fossiliferous sandstones of the past. 



One of the chief causes of the destruction of animal life on 

 plains of subaerial deposition is found in the periodic droughts 

 affecting these regions. The geologic effects of such droughts 

 have been noted in many tropical countries, especially along the 

 west coast of Africa, in India, and in South America. Darwin 

 (17) has described the "gran seco" or great drought which occurred 

 between the years 1827 and 1830, when, in the northern part of the 

 province of Buenos Ayres (South America) and the southern part 

 of St. Fe, vast numbers of birds and animals perished, the vegeta- 

 tion withered and died, and the brooks became dry, until finally 

 the whole country was turned into a dusty, waterless waste. Dar- 

 win writes : "A man told me 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. The lowest estimation of 

 the loss of cattle in the province of Buenos Ayres alone was taken 

 at one million head. A proprietor at San Pedro had previously 

 to these years 20,000 cattle, at the end not one remained. 



"I was informed by an eye-witness that the cattle in herds of 

 thousands rushed into the Parana, and being exhausted by hunger 

 they were unable to crawl up the muddy banks and thus were 

 drowned. . . . Without doubt several hundred thousand ani- 

 mals thus perished in the river : their bodies when putrid were 

 seen floating down the stream ; and many in all probability were 

 deposited in the estuary of the Plata. All the small rivers became 

 highly saline, and this caused the death of vast numbers in particu- 

 lar spots ; for when an animal drinks of such water it does not 

 recover. . . . Subsecjuently to the drought of 1827 to '32 a 

 very rainy season followed which caused great floods. Hence it is 

 almost certain that some thousands of the skeletons were buried by 

 the deposits of the very next year." Darwin adds very pertinently, 



