Page:The Journal of geology (IA journalofgeology21894univers).pdf/399

To the ancient Greeks the word epeiros, specially applied to the land lying next north, signified also, in general, any mainland or continental area, as contrasted with islands or their own peninsular country. From this word Gilbert has recently supplied to our science the terms epeirogeny and epeirogenic, to designate the broad movements of uplift and subsidence which affect the whole or large parts of continents and of the oceanic basins.^[2] Previously the correlative terms orogeny and orogenic had come into use, denoting the process of formation of mountain ranges by folds, faults, upthrusts and overthrusts, affecting comparatively narrow belts and lifting them in great ridges, while the epeirogenic movements of the earth's crust produce and maintain the continental plateaus and the broad depressions which are covered by the sea.

During the closing part of the Tertiary era and the present Quaternary or Psychozoic era, both epeirogenic and orogenic changes have been in progress on many portions of the earth, and on a scale of grandeur probably never before surpassed. Where these movements have raised continental regions or mountain districts to much greater altitudes than they now retain, if they were situated within the range of prevailing air currents abundantly laden with moisture and were at latitudes so far from the equator that the precipitation was chiefly snow throughout the year, they became for a time enveloped by ice-sheets, which have left the surface strewn with glacial and modified drift. Fjords, and now submarine continuations of river