Page 4 Advertisements Column 1

Ashburton Guardian, Volume IV, Issue 1013, 30 November 1883, Page 4

Mr Richard A. Proctor writes as follows on the subject of earthquakes :—Since the terrible disaster at Ischia the general subject of subterranean disturbances has been much discussed in our daily and weekly papers, but for the most part without much knowledge of the conditions on which the occurrence depends. It seems generally supposed of earthquakes and volcanic eruptions that subterranean disturbances are caused by internal heat, and by the movement within the earth of great masses of compressed vapor and molten matter. Th : s is to mistake cause ‘and effect Almost alt forms of vulcanian disturbances are due to subterranean heat by which displacements are caused. The trne'.source of the forces at work In earthquakes and eruptions is terrestrial gravity acting on the substance of the earth’s crust and causing it to be drawn inwards wherever the resistances to su.-h motion are overcome. Mallet and Dana have, indeed, shown that heat was an important factor in those great vulcanian movements which may be regarded as cosmical in importance, those two earlier stages of the earth’s vulcanian history during which, first, the crust shrank more quickly than the nucleus and was rent by the resistance of this central mass ; and later, the nucleus contracted more quickly than the crust, which had to Cose in upon the centra! mass in a aeries of wrinklings or corrugations. But even then the action of gravity was the chief cause of the. changes wrought. In the i resent or third stage of the earth’s vulcanian history, matters have been altered. The direct action of heat is no longer the cause of subterranean activities, but the indrawing action of gravity, and the grinding of rock masses against each other in those parts of the earth’s crust (nearly all of them close by water) where the equilibrium is least secure and the internal resistances are least regular.

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