Professor J. Joly, in his interesting paper estimating the geological age of the earth from the amount of sodium contained in the sea, mentions in an appendix seven possible errors which may render his estimate a minimum, and seven others which may render it a maximum. Neither among the former errors guarded against in the appendix, nor in the body of the paper, does there appear any reference to the possibility of sea-water being absorbed by the surface rocks of the globe, either by capillary attraction, as maintained by Daubrée, or by means of fissures, as contended by De la Beche.