Distorted Mountain Strata in Relation to Final Isostasy

Abstract

ISOSTATIC equilibrium ensues only after disturbances have ceased. The strata of mountains must originally have been deposited horizontally. They may be held to have attained to heights much greater than now exist. As they accumulated locally gravity would be disturbed by their weight, and if they rested on a much deeper foundation of slightly viscous but more dense material they would gradually sink down into it until they floated in hydrostatic equilibrium. It is assumed that this sinking is a slower process than the deposition of the strata. As the result, if a level datum surface is imagined as traced in the viscous foundation, at a level below the sunk roots of the deposited strata, hydrostatic equilibrium along it requires that the weight of material in all columns standing on this surface should be uniform. This is the observed isostasy ; thus, beneath a more elevated region its roots of lighter density would penetrate deeper and so compensate the extra column aloft. The depths of these floating roots should even exceed the heights of the elevations, so the height of the original deposited strata would have been much greater than that of the present compensated mountains. In the deep sinking of such horizontal local strata they would be broken up, with result reminiscent of the distorted fragmentary mountain strata that are observed. But an analogy to the breaking up of an Arctic ice-floe would be excessive.