Distortion of Mountain Strata, Isostasy, and Glacial Periods

Abstract

THE connexion of the distorted mountain strata with isostasy has been examined in NATURE of April 2, p. 603. The foundation of the argument was that the strata were originally deposited horizontally at the bottom of the sea. It is, however, necessary to go further back, for they must have been lifted to a great height before isostatic influences could begin to operate. There is here a problem of flow in a medium of extremely viscous type, namely, the outer region of the earth beneath, which can scarcely be avoided. If anywhere the horizontal drift beneath is from both sides towards the same centre the lighter material above it will be pushed up as is required, and in part also pushed down, but the resulting displacement need not at first be isostatically distributed. So also at ocean deeps the underlying drift away from the centre may carry along the more solid upper strata, thinning them out: anyhow a problem presents itself there. Moreover, in all internal motions the drift relative to the surface is necessarily tangential. The analogy of the sideway shrinking up of a flat roll of cloth has been employed.