T. M. Reade—Denudation of the two Americas. 293 
ment by Mr. Bateman, 520,000 cubic feet of water to the La 
Plata, while the Uruguay was estimated at only 150,000 cubic 
feet at the same time, it follows that the chemical constituents 
of the water of the La Plata must vary considerably at different 
times and seasons. Probably the analysis on which I have 
made my calculations will represent a fair annual mean of the 
solids in solution. 
The estimated drainage area of these two rivers is 1,250,000 
square miles, so that were the mean annual discharge known 
it would probably turn out that the greater discharge of the La 
Plata would more than compensate for the smaller per centage 
of dissolved matters in its waters and bring the chemical 
denudation per square mile of river basin up to or beyond that 
of the Mississippi. 
e observations of Mr. Bateman were taken in the month of. 
December, 1870, when the river was at its lowest state. “A 
continuous drought of six or seven months having diminished 
the ordinary sources of supply and the periodical rise from the 
Andes not having commenced.” It is difficult, nay, impossible, 
to predict the mean delivery from the dry weather flow, but 
the mean flow of the Rhine is given by Beardmore as over 
twice, the Rhone at Avignon nearly three times, and the Nile 
at Cairo over seven times the ordinary summer flow. 
he waters of the La Plata are distinguished by the fineness 
of the matter held in suspension; this consists, according to 
Mr. Kyle, principally of clay. This clay continues a long time 
in suspension even after filtering. It will pass through the 
pores of the best filtering papers, the water preserving its tur- 
bidity even after months of repose. This isa feature according 
to Mr. Kyle which is common to all waters that are weakly 
alkaline. Several chemicals added to the water will, however, 
precipitate the solid matter by making the muddy particles 
Coagulate into larger compound particles. Chloride of calcium 
in the proportion of 1 to 5,000 parts will act in this manner. 
The analyses given by Mr. Kyle are of the water after 48 hours 
subsidence, so that the unprecipitated matter is included in the 
Solids in solution. The matters in suspension, as is the case with 
other rivers, vary much according to the state of the river and 
the water is more impure near the shore than at 850 m. distant. 
It is pretty well known that an admixture of seawater with 
turbid fresh water tends to hasten the precipitatiow of the solid 
matters* but it is very probable, as will be seen before I con- 
clude, that the extremely divided solid matter will be carried 
ar and wide by oceanic currents before it can settle to the 
bottom. 
* See “precipitation of Clay in fresh and salt water,” by D. Robertson, Trans. 
Glasgow Geol. Soc., vol. iv, Part III, page 257. 
