Since Dutton’s exposition of the principle of isostasy, in 1889, the advance of geologic knowledge has made more and more probable, in a general sense, the reality of isostatic adjustment in the earth. Nevertheless there has been, and yet is, considerable diversity of opinion among geologists regarding the degree of its completeness, the depth at which it is effective, and the mechanisms involved in its accomplishment. Recent discussions by Barrell,1 Leith,2 and Willis3 may serve to illustrate this. Moreover, so far as the present writer is aware, no one (except himself,4 and he only partially and tentatively) has invoked the principle, on strictly geologic grounds, to explain relations existing among crustal units of small area, or conditions affecting such units. And earlier opinion was distinctly adverse to this.
Geodetic Establishment of isostatic Equilibrium
On the other hand, recent geodetic work, especially that conducted by Hay ford5 and . . .