WHAT VOLCANOES ARE NOT.

South Canterbury Times, Issue 2745, 10 January 1882, Page 3

WHAT VOLCANOES ARE NOT.

“ What is a volcano ?” This is a question, often addressed* to ns in our youtli, which “.Catechisms of Universal Knowledge,” and similar school manuals, have taught us to reply td in'some such terms as'’tlie following : “ A volcano is a burning mountain, from the sohi'mit of which issue smoke and flames,” , This description, says Professor Judd, is not merely incomplete and inadequate, as a whole, but each individual proposition of which it is made up is grossly inadequate and, what is wo^sef,-perversely misleading. In the first place, the action which takes place at' volcanoes isj not “ burning,” or combustion, and bears, indeed, no relation whatever to that well-known process. Nor are volcanoes necessarily “ mountains ” at all esieritiallfi' they are just the revefse---namcly, holes in the earth’s crust, or outer portion, by means of which a communication ds kept top between the surface and the interior of the, globe. When mountains do exist at' centres of .yolcajiic aQtjyi ;{ ;they. are < ..;sirqply the heaps of materials thrown out of these hales, 'atod ‘itonst, therefore, :i he re? garded not as causes but as the, consequences of volcanic action. Neither does this potion always takeplaccat the “summit” of volcanic mountains when such exist, tor eWptions occur quite as frequently on .their sides or at their base. That, too, which popular fancy regards as- is ; really condensing steam of watery vapor, and the supposed raging “ flames ” are nothing more: than«the glowing .light of a mass of molten material reflected from these vap&f-dbiids. ■ r■ -