I.—Note in Explanation of Plate VII., to Illustrate the Theory of Subsidence and Elevation of Land, and the Permanence of Oceans

Extract

Fig. 1 is intended to represent a section across an ocean basin. It is supposed that the combined weight of water (1) and sediment (2), acting upon an elastic layer of rock (3), compresses the fluid layer which underlies it (4), and forces it to escape laterally, and either to accumulate and partially solidify, thus raising the crust above; or, where the tension is extreme, and the resistance inadequate, to form fissures or vents. The continuously sustained pressure towards the centre of the basin constantly converts fresh solid into fluid, which escapes again and again, perhaps at intervals of centuries, causing fresh upheavals or eruptions, perpetually deepening the ocean basin.