It is doubtful if the Earth’s crust exceeds, or equals 1,000 miles in thickness. The outside is held from flying to pieces by the atmosphere, which is a sort of tire to the earth, while the inside is constantly pressing from effect of centrifugal force. These two factors must meet somewhere.
On the outside, near the ice belt, the water pressure gets the best of the inner forces and drives the waters into Symmes’s Hole. In the Earth the centrifugal force has advantage until reaching the surface; but if a big hole could be cut at the Equator through to the center, no doubt a man could jump into it in safety and cease to fall as he cushioned against centrifugal influence in his descent. Earthquakes are only the effects of internal pressure of water to get to the surface, at times bursting large reservoirs, producing tremblings, and at others with great force throwing up hills and mountains from the tops of which the fountains of water burst forth. At other times they are produced by the contact of water with heated elements in volcanoes, creating the commotion leading to the volcanic eruption, the latter of which can only be produced by contact of fire and water.
It is believed that this is the complete and brief explanation of earthquake causes.