“Volcanism is still one of the most inexplicable and profound problems which defy the power of geologists to explain, and one of its most singular peculiarities is the fact that it sometimes breaks forth simultaneously in widely distant portions of the earth. A sympathetic relation of this kind has long been known between Hecla and Vesuvius, and it is very probable that the Carib volcanoes have some such sympathetic relation with the volcanoes of Central America and southern Mexico. At the time of the explosion of St. Vincent other explosions preceded or followed it in northern South America and Central America.
“The outburst of Mount Pelee, in Martinique, is apparently the culmination of a number of recent volcanic disturbances which have been unusually severe. Colima, in Mexico, was in eruption but a few months previous, while Chelpancingo, the capital of the State of Guerrero, was nearly destroyed by earthquakes which followed.
“Only a few days before Mount Pelee erupted, the cities of Guatemala were shaken down by tremendous earthquakes.”
Professor N. S. Shaler, of Harvard University, a world authority on volcanic disturbances, says:
“Volcanic outbreaks are merely the explosion of steam under high pressure—steam which is bound in rocks buried underneath the surface of the earth and there subjected to such tremendous heat that when the conditions are right its pent up energy breaks forth, and it shatters its stone prison walls into dust.
“The common belief is that water enters the rocks during the crystallization period, and that these rocks, through the natural action of rivers and streams, become deposited in the bottom of the ocean. Here they lie for many ages, becoming buried deeper and deeper under masses of like sediment, which are constantly being washed down upon them from above. This process is called the blanketing process.
“When the first layer has reached a depth of a few thousand feet the rocks which contain the water of crystallization are subjected to a terrific heat. This heat generates steam, which is held in a state of frightful tension in its rocky prison.
“It is at these moments that volcanic eruptions occur. They result from wrinkling in the outer crust of the earth’s surface—wrinklings caused by the constant shrinking of the earth itself and by the contraction of the outer surface as it settles on the plastic center underneath. Fissures are caused by these foldings, and as these fissures reach down into the earth the pressure is removed from the rocks and the compressed steam in them and it explodes with tremendous force.
“The rocks containing the water are blown into dust, which sometimes is carried so high as to escape the power of the earth’s attraction and float by itself through space. After the explosions have occurred lava pours forth. This is merely melted rock which overflows like water from a boiling kettle. But the explosion always precedes the flow, and one will notice that there is always an outpouring of dust before the lava comes.”
Professor W. J. McGee, of the Smithsonian Institution at Washington, says: “It may be that a violent earthquake tremor came after the volcanic eruption, but it does not necessarily follow that the two travel together. Oftentimes we hear of earth tremors with no apparent accompaniment. This was true of the Charleston earthquake in 1886. Earthquakes are caused by mysterious disturbances in the interior of the earth. The most commonly accepted belief is that massive rock beds away down in the earth, at a depth of twelve miles or more, become disturbed from one cause or another, with the result that the disturbance is felt on the earth’s surface, sometimes severely, sometimes faintly.