296 ZT. M. Reade—Denudation of the two Americas. 
This gives a oe ae of total solids insolution of zy455 OF 
5:1 tons per second. 
The total delivery of matters in solution will amount, accord- 
ing to these data, to 160,833,600 tons per annum, or, if we esti- 
mate the basin at 3,000,000 square miles, to 60 tons per square 
mile per annum. 
It will be observed that the total amount delivered to the sea 
of solids in solution is not much greater than that we arrived at 
for the Mississippi. This is a fact worth knowing and due 
doubtless to the preponderance of gneissic rocks and sandstones 
and clays of an insoluble character. It is also worth noting 
that the proportion of silica to the total matter in solution cor- 
responds very closely with that of the Mississippi, amounting to 
26,624,481 tons per annum. It is also evident that the rocks 
and Pampean deposits* occupying the basin of the La Plata 
are also of a more calcareous and soluble character than the 
Amazonian Rocks. Not less interesting is it that the carbon- 
ate of lime. roughly speaking, is one half. of the whole of the 
solids in solution. 
It follows from these data that the matter removed in sus- 
pension must bear an excessive proportion to those in solution 
comparing the Parad and the main Amazons, saya, ‘In the 
former the flow of the tide always creates a strong current Up- 
wards, while in the Amazons the turbid flow of the mighty 
stream over-powers all tides, and produces a constant down- 
ward current. The color of the water is different, that of the 
Para being of a dingy orange-brown, while that of the Amazons 
has an ochreous or yellowish clay tint,” also ‘Indeed the fresh 
water tinges the sea along the shores of Guiana to a distance of 
nearly 200 miles from the mouth of the river.”t 
INFERENCES AND GENERALIZATIONS. 
In my former address I said, “ Taking into consideration 
what we know of the geology of the world, I think we have 
sufficient grounds for a provisional assumption that about 100 
tons of rocky matter are dissolved by rain per English square 
mile perannum.”§ This at the time was considered a very bold - 
statement, but from the data I have laid before you respecting 
the American continents I venture to think it will be now con- 
* See Geological Observations, Darwin, Second Edition, pp. 313 to 369. 
See Chemical Denudation, p. 24, + Naturalist on the Amazons, vol. i, p- 5- 
Chemical Denudation, p. 24. 
