Plastic Flow — or Plastic Reasoning ?

In the April 7th issue of Salient there appeared a summary of a talk by Dr. F. Everson (Geophysics Division—D.S.I.R.) to the Maths and Physics Society.

The summary was entered by the society and contained a certain amount of sarcasm directed towards geologists, who cannot for obvious reasons accept Dr. Ever son's theory. This theory, which postulates continents flowing laterally under their own weight on a rigid substratum—presumably the Simatic upper surface—has many glaring objections.

However, in view of the sarcasm directed at geologists, I feel obliged to point out that while a theory may be applicable in terms of Maths and Physics, it is the practical application which either makes or—in this case—breaks it.

Firstly, physical evidence of the Sial-Sima boundary (Sial and Sima layers constitute the crust of the earth) indicates anything but a rigid substratum. Secondly, if a rigid substratum existed how do horizontal stresses develop in the outer crust as evidenced by folding of strata during orogeny—say New Zealand's Southern Alps?

Also submarine canyons could not possibly be formed by gradual submergence of river canyons at Dr. Everson's suggested rates of movement, as wave erosion would have ample time to destroy them.

Other objections, possibly more fundamental than these, become too technical for the purposes of this paper, so with all due respects to Dr. E. I would point out that the Mathematicians and Physicists do not have it all their own way and a little more down-to-earth thinking might produce more plausible results.