There are many reasons for believing that the floor of the oceans, at least of the Pacific, consists of basaltic rocks as distinct from the granitic rocks which form the continents. It is here suggested that this non-uniform distribution of rocks over the earth’s surface may have been caused by the particular kind of cooling mechanism which was adopted in the early stages of the earth’s history. A stage would be reached when granite would separate out as a lighter mass resting on the heavier and still liquid viscous basalt.