Parr L] THE OCEANS. 33 
- any large mass of land are of volcanic origin and contain no ancient 
formations. St. Helena and Ascension in the Atlantic, and the Friendly 
and Sandwich Islands in the Pacific Ocean are conspicuous examples. 
The water of the oceans is distinguished from ordinary terrestrial 
waters by a higher specific gravity, and the presence of so large a 
proportion of saline ingredients as to impart a strongly salt taste. 
The average density of sea-water is about 1:026, but it varies 
slightly in different parts even of the same ocean. According to the 
recent observations of Mr. J. Y. Buchanan during the Challenger 
expedition, some of the heaviest sea-water occurs in the pathway of 
the trade-winds of the North Atlantic, where evaporation must be 
comparatively rapid, a density of 1:02781 being registered. Where, 
however, large rivers enter the sea, or where there is much melting 
ice, the density diminishes; Mr. Buchanan found among the broken 
ice of the Antarctic Ocean that it had sunk to 1:02418. 
The greater density of sea-water depends of course upon the salts 
which it contains in solution. At an early period in the earth’s 
history the water now forming the ocean, together with the rivers, 
lakes and snowfields of the land, existed as vapour, in which were 
mingled many other gases and vapours, the whole forming a vast 
atmosphere surrounding the still intensely hot globe. Under the 
enormous pressure of the primeval atmosphere the first condensed 
water might have had the temperature of a dull red heat. In con- 
_densing, it would carry down with it many substances in solution. 
The salts now present in sea-water are to be regarded as principally 
derived from the primeval constitution of the sea, and thus we may 
infer that the sea has always been salt. It is also probable that, as 
in the case of the atmosphere, the composition of the ocean water has 
acquired its present character only after many ages of slow change, 
and the abstraction of much mineral matter originally contained in 
it. There is evidence indeed among the geological formations that 
large quantities of lime, silica, chlorides, and sulphates have in the 
course of time been removed from the sea. 
But it is manifest also that, whatever may have been the original 
composition of the oceans, they have for a vast section of geological 
time been constantly receiving mineral matter in solution from the 
land. Every spring, brook, and river removes various salts from the 
rocks over which it moves, and these substances, thus dissolved, 
eventually find their way into the sea. Consequently sea-water 
ought to contain more or less traceable proportions of every substance 
which the terrestrial waters can remove from the land, in short, of 
probably every element present in the outer shell of the globe, for 
there seems to be no constituent of the earth which may not, under 
1 Buchanan, Proc. Roy. Soc. (1876), vol. xxiv. 
2 Q. J. Geol. Soc. xxxvi. (1880) pp. 112, 117. 
3 Dr. Sterry Hunt even supposes that the saline waters of Canada and the northern 
States derive their mineral ingredients from the salts still retained among the sediments 
and precipitates of the ancient sea in which the earlier Paleozoic rocks were deposited. 
— Geological and Chemical Essays, p. 104. 
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