CHAPTER IX
THE FLOOR OF THE OCEAN
We have seen above that in the most rapid continental displacements there is only a question of an annual increase of about 10 m. in a distance of about 1000 km. If this amount of 10 m. be uniformly distributed over the whole distance, then each metre would show an increment of 0.01 mm. in the year. This is a very small quantity. Since the rock of the oceanic floor will naturally be intersected by all kinds of cracks, a very trifling expansion of these fine fissures would be sufficient to extend the total distance the required amount. In the deeper layers the sima would, without difficulty, be stretched about this amount. It is thus not necessary for the molten sima ever to come to the surface during this whole process. It is, however, on the other hand, probable that these processes take place irregularly. At one place the surface would receive no increment, in another the increase would, in compensation, be so much greater. And thus, at least here and there, highly heated portions of the sima would be uncovered.
But it need not be assumed that the outcropping of such highly heated material on the sea-floor would be attended with anything like catastrophic events. The “critical pressure” of water only amounts to 200 atmospheres, and will therefore be reached at a depth of 2000 m. Thus, however great the heat, no
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