On the Annual Water-discharge of Large Rivers. 263 
tales wide. At Buenos Ayres, 100 miles from the sea, 30 miles 
wide ; and just below the junction of the various mouths of the 
Parana with the Uruguay, 120 miles from the sea, it is 26 miles 
wide. The volume of fresh water it conveys to the sea is proba- 
bly exceeded only by the Amazon. 
“The total area of the basin has been estimated at 1,250,000 
square miles*. The Parana, its chief feeder, takes its rise in 
Brazil, within the tropics, and is swollen by the tropical rains of 
that region, At about 27° S. latitude it is joined by its most. 
_ important tributary, the Paraguay. Some of the branches of this 
river extend to within 12° of the equator, and are also fed by 
tropical rains; while. others issue from the Cordilleros de los 
Andes, and are periodically swollen by the melting of the snows 
which rest on the high points of that range of mountains. For 
700 or 800 miles, these mountains shed the waters which fall on 
their eastern slopes to the Paraguay or the Parana, and some 
smaller streams from the lower lands of the province of 
Buenos Ayres enter the Plate near the embouchure of the 
Parana. 
“The Uruguay, the other great tributary of the Plate, descends 
from the central part of South America, draining a vast area, and 
swollen periodically by tropical rains. 
“The detritus, or suspended matter, brought down by these 
streams, has formed the delta of the Parana, the islands which 
are clustered about its various mouths, and the shoals of the 
River Plate. 
“Tt was considered a matter of great importance, as bearing 
directly upon the question of the practicability of improving the 
harbour accommodation of Buenos Ayres, to ascertain the volume 
of these streams, and the quantity of matter which they carried 
in suspension. 
“For this purpose careful measurements have been made 
during the month of December, 1870. 
“The Parana was in its lowest state—a continuous drought of 
six or seven months having diminished the ordinary sources of 
- supply, and the periodical rise resulting from the melting of the 
- snows of the Andes not haying yet commenced. This river is 
* This is equivalent to 968,000 sq. geo. miles. 
