| OCR Text |
Show 142 GEOLOGY OF THE HIGH PLATEAUS. rences which take place in waters and in their vicinity. It has long been held that water plays an essential part in volcanic eruptions, and it is quite natural that we should infer from the association that the penetration of water to the internal fires is after all the determinant; but, on the other hand, we cannot leave out of view the fact that there is water on the land as well as in the sea, and that every year from 30 to 50 inches of rain are ordinarily poured over the surface and the underground water-ways and fissures are kept full. An abundant penetration may, therefore, take place on land as well as under the sea. It does not seem justifiable, therefore, to conclude that the mere presence of water is the sole determinant. There is, however, one class of processes peculiar to bodies of water. It is beneath their surfaces that sediments are accumulated, often to the thickness of thousands of feet, until by their gross weight they subside. It may be that the ultimate cause of volcanism will eventually be traced to the shifting of vast loads of matter from place to place upon the earth's surface, but at present this subject has not been investigated from a mechanical standpoint with sufficient method and system to admit of safe generalization or even of legitimate speculation. The assumption that a rise of temperature is the proximate cause of volcanic energy, then, is not a wholly arbitrary postulate, but is consistent with a wide range of facts; brings into order not only the broader but also the subordinate facts of volcanology, and apparently affords a working hypothesis. |
