Note 35 — Chapter VI
Reading edition
The stratum of constant temperature runs in a wave-like form from pole to pole. In the arctic and antarctic oceans it is found at a depth of 4500 feet, whence it slopes upwards so as to reach the surf ice at the temperate zone on both sides of the equator. It then gradually sinks down in the warmer regions, till at the equator it is 7200 feet below the sea-level. There are thus one tropical and two polar basins separated by two wave-like circles, or, as a geologist would say, three synclinal troughs separated by two anticlinal ridges.