The thesis may be considered a corollary of Gutenberg's theory of continental spreading. The paper should be read in conjunction with those by Gutenberg.

Few assumptions are required if it be granted that our distinctions between solid and liquid are artificial and expedient rather than actual and that what we term solids may flow with a time factor which is great and may approach infinity. It must be assumed also that the original crust of the earth was of sima and that the lighter sial was formed from it.

A compromise is effected between the concepts of permanence of continental masses and of instability and movement relative to one another. For the causes which produce the elevations and depressions on the original sial sheets are such as might permanently affect such parts of the sheets. Thus both original land areas and water-filled depressions would be persistent though they would tend to increase in area with the spreading of the sheets. Changes of form would take place as isostatic conditions became affected locally both by added loads of light sediments deposited by the ordinary agencies and by the thinning of the sheets in other places by erosion. The land bridges between continents required by Schuchert and Bailey Willis are easier to account for if we regard the continental m sses as being closer together when these bridges existed and the consequent foundering of such bridges would necessarily follow upon the stretching of the sial sheets as the masses drew farther apart. Again, some of the land bridges may have been due to the local junctioning of irregular-shaped sial sheets moving in opposite directions from the polar regions.