Isostasy

Abstract

In scientific literature of to-day dealing with geophysical matters one frequently meets assertions that the hypothesis of isostasy is universally established. Prof. Heiskanen begins a recent article,¹ “In recent years geodesists, geophysicists, and geologists have studied extensively isostatic compensation and it can be considered as a proved fact that isostatic compensation prevails, at least in North America (Hayford, Bowie), in India (Pratt, Airy, Burrard, Crosthwait), etc.”. I consider this statement far from true as regards India. Pratt and Airy, whose work is published in the Phil. Trans. Roy. Soc. (1854–59), had only three values of the meridian value of the deflection of the vertical on which to base their studies. Pratt suggested the idea of mountain compensation; but he did not completely satisfy the observational points. Burrard in 1901² did not agree with Pratt's conclusion; later on, however, in 1918,³ by extending the scope of Hayford's isostatic hypothesis to include compensation of density anomalies, he was able to satisfy the observational data then existent in the Himalaya and neighbouring regions by attributing appropriate depth to such anomalies. Crosthwait in 1912⁴ wrote: “Speaking generally, it would appear that isostatic conditions are much more nearly realised in America than in India”. He had made the necessary calculations for the Hayford deflection at 102 latitude stations and 18 longitude stations distributed over India.