CAUSE OP THE EIVER-FLOODS. 11 



with the Rio Guaviare, the source3 of the Orinoco were 

 sought towards the south-west, on the eastern back of the 

 Andes, the risings of this river were attributed to a perio- 

 dical melting of the snows. This reasoning was as far from 

 the truth as that in which the Nile was formerly supposed 

 to be swelled by the waters of the snows of Abyssinia. The 

 Cordilleras of New Grenada, near which the western tribu- 

 tary streams of the Orinoco, the Guaviare, the Meta, and 

 the Apure, take their rise, enter no more into the limit of 

 perpetual snows, with the sole exception of the Paramos of 

 Chita and Mucuchies, than the Alps of Abyssinia. Snowy- 

 mountains are much more rare in the torrid zone than is 

 generally admitted; and the melting of the snows, which is 

 not copious there at any season, does not at all increase at 

 the time of the inundations of the Orinoco. 



The cause of the periodical swellings of the Orinoco acts 

 equally on all the rivers that take rise in the torrid zone. 

 After the vernal equinox, the cessation of the breezes 

 announces the season of rains. The increase of the rivera 

 (which may be considered as natural pluviometers), is in 

 proportion to the quantity of water that falls in the different 

 regions. This quantity, in the centre of the forests of the 

 Upper Orinoco and the Rio Negro, appeared to me to exceed 

 90 or 100 inches annually. Such of the natives, therefore, 

 as have lived beneath the misty sky of the Esmeralda and 

 the Atabapo, know, without the smallest notion of natural 

 philosophy, what Eudoxus and Eratosthenes knew hereto- 

 fore,* that the inundations of the great rivers are owing 

 solely to the equatorial rains. The following is the usual 

 progress of the oscillations of the Orinoco. Immediately 

 after the vernal equinox (the people say on the 25th of 

 March) the commencement of the rising is perceived. It 

 is at first only an inch in twenty-four hours ; sometimes the 

 river again sinks in April ; it attains its maximum in July ; 

 remains at the same level from the end of July till the 25th 

 of August; and then decreases progressively, but more 

 slowly than it increased. It is at its minimum in January 

 and February. In both worlds the rivers of the northern 

 torrid zone attain the greatest height nearly at the same 

 period. The Ganges, the Niger, and the Gambia, reach the 



* Strabo, lib. 17, p 789. Diod. Sic., lib. 1, c. 5. 



