Page:The Journal of geology (IA journalofgeology21894univers).pdf/236

The doctrine of isostasy has been tentatively accepted by many working geologists. It finds application in various departments of geology, but nowhere more conspicuously than in glaciology. Without passing judgment on the doctrine, and without attempting to restrict the field of its application, attention is called to a misapprehension to which it has given rise. This misapprehension is widespread in the popular mind, and has even found a foothold among those who have given attention to glacial geology.

Among the hypotheses which have gained more or less currency in explanation of the Pleistocene glacial climate, is that of northward elevation. Whatever may be thought of this hypothesis from a priori considerations, or whatever may be thought of the evidence which is adduced in support of it, it has come to have an appendix which we believe to be false. This appendix seems not to have accompanied the hypothesis at the outset, and some of the advocates of the hypothesis do not appear to have given their sanction to the appendix, though their names are sometimes connected with it.

The hypothesis is, that northward elevation lowered the temperature of the region affected to such an extent as to occasion the accumulation of the Pleistocene ice-sheet. The appendix is, that the elevated area sank under the weight of ice for which it was responsible, until, as a result of the sinking thus effected, the climate was so far ameliorated as to bring about the melting of the ice-sheet and the end of the glacial period. The appendix is sometimes stated in milder form, the depression resulting from the weight of the ice being looked upon as only one of the causes which brought about the dissolution of the ice-sheet. This view, both in its wider and in its more restricted sense, we