26 A. Tylor on Changes of the Sea-Level effected by 
out rain. Since there must be extensive districts which contribute 
no detritus whatever to rivers, | propose to assume that one-half 
the earth’s surface only is drained by rivers flowing directly into 
the sea,* and that the average supply of detritus does not excee 
that afforded by the district through which the Mississippi flows (a 
country where there are no very high mountains, and only a 
moderate quantity of rain). 
The quantity of soluble salts annually carried into the ocean 
must amount to a very large volume, particularly as river-water 
always contains matter in solution, while it is only during two or 
three months of the year that alluvium in suspension is carried 
down in large quantities. The proportion of soluble salts in the 
water of the Thames is 17 to 70,000, or 1 to 4117; while the 
proportion of alluvium suspended in the water of the Mississippi 
is as 1 to 3000. 
The level of the land is as much reduced by what is carried 
away in solution, as if this were mud and sand removed in sus- 
3 feet and raise that of the ocean 1 foot. It was during the con- 
templation of the changes of level that might have been pro- 
duced by the operations of ordinary physical agents upon the sul- 
face of the earth, that Hutton was led to remark that it was not © 
necessary to suppose the area of the land always maintained the 
drain 
ers running into European lakes and inland seas oth a be seen. He 
issippi River, see Sir Charles Lyell’s Second Visit 
5 


SSISS 
to the United States, edit. 1847, vol. ii, p. 249 to 253, and other places, 
4M Balbi shows (Atlas, Soc. Diff. Useful Knowledge, 1844) that the land on the 
sabe equals 37,547,000 square geographical miles, the sea equals 110,875,000 squar 
eran Ee : fs : 
a ate ay 
* By a to Johnston's Physical Atlas, the calculated portion of land 
1e TL . ‘ 
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