It is generally accepted that the continents contain more radio-activity than the Pacific floor. The two continents, Laurasia and Gondwanaland, would therefore expand the rocks below, relative to that floor. The plastic substratum under the continents would be forced higher in their centres than at their centres than at their Pacific margins. It would creep towards those margins and would carry part of the overlying granite to them, piling it high at their margins and thinning it at their centres. The plastic substratum would continually carry its heat to the cold Pacific substratum and render it plastic into which the continents would be impelled.