Note 107 — Chapter XI · TO HEKLA AND THE GEYSIR IN HAUKADALR.[87]

Especially M. Dortous de Mavian, whose theory was succeeded by the age of chemicals, pyrites, and alkalis, and the oxidation of unoxidised minerals, with a brief deversion in favour of “The Fire,” by Sir Humphrey Davy. Poisson extinguished it when he remarked that if fed by incandescent gases it would burst the shell, or at least would be subject to tides, causing daily earthquakes. Happily, also, the term “earth’s crust” is also becoming obsolete, or rather the solid stratum of 100 miles overlying a melted nucleus has suddenly grown to 800 (Hopkins). Sir William Thomson (Proceedings of the Royal Society, xii., p. 103) holds it “extremely improbable that any crust thinner than 2000 or 2500 miles could maintain its figure with sufficient rigidity against the tide-generating forces of sun and moon, to allow the phenomena of the ocean tides, and of precession and nutation, to be as they are now.” We will hope for more presently.