supposed to be the cause of the blue color to the sky ; and in a vesicular form, in which state it constitutes the clouds. Terrestrial water forms about three-fourths of

the surface of the terraqueous globe. The average depth of the ocean is calculated at between two and three miles. Now as the height of dry land above the surface of the sea is less than two miles, it is evident, that if the present dry land were distributed over the bottom of the ocean, the surface of the globe would present a mass

of waters a mile in depth. On the supposition that the mean depth of the sea is not

-- ;

greater than the fourth part of a mile, the solid contents of the ocean would be

32,058,939 cubic miles ( Thomson's Chemistry.) The quantity of water mechanically disseminated through rocks, which serve merely as a natural reservoir for the time, must be, in the aggregate, very considerable, though it is impossible to form

any very accurate estimate of it. Even in those rocks which merely supply springs, the amount of disseminated water must be enormous ; for they so far resemble filters, that are necessarily charged with the fluid before they permit it to pass out.

De La Beche has advanced the opinion that capillary attraction has great power, both in mechanically disseminating water among rocks, and in retaining it in them when so disseminated, and that it therefore keeps them, to a certain extent, saturated with moisture, and assists in promoting a more equal flow of water in springs.