412 REACTION OF THE INTERIOR OF THE EARTH 



I have already referred, in an earlier volume (Kosmos, 

 Bd. i. S. 454, Engl. ed. vol. i. note 234), to the com- 

 plicated theory of Trogus Pompeius, under Augustus, 

 according to which the salt water of the sea is supposed 

 to stimulate the volcanic fire. Different chemical and 

 mechanical causes of the influence of the neighbourhood 

 of the sea have been adduced up to the most recent times. 

 The ancient hypothesis of the penetration of sea-water 

 to the volcanic hearth seemed to have acquired a more 

 solid foundation at the epoch of Davy's discovery of the 

 metallic bases of the earths; but the great discoverer 

 himself soon gave up that hypothesis, to which even Gray- 

 Lussac had been inclined ( 564 ) notwithstanding the rarity 

 or entire absence of hydrogen gas. Mechanical, or rather 

 dynamical causes, whether they should be looked for in 

 the folding of the earth's outer crust and the upheaval 

 of continents, or in the locally lesser thickness of that 

 crust, would seem, according to my ideas, to present a 

 greater degree of probability. We may readily repre- 

 sent to ourselves the probability that, at the margins of 

 the upheaving continents, whose coasts now rise with 

 more or less abruptness above the waters of the sea, 

 simultaneously occasioned subsidence of the ocean-bed 

 might cause the formation of fissures tending to pro- 

 mote communication with the molten interior. In the 

 inland parts of elevated continents, at a distance from 

 the oceanic areas of subsidence, there would not be the 

 same occasion of fracture. Volcanoes follow the coast- 

 lines in single, sometimes in double, and even triple 

 ranges. Short cross ridges, elevated over cross fissures, 

 connect these ranges, forming mountain-knots. Fre- 

 quently, but by no means invariably, it is the outer 

 range, nearest to the sea-shore, which is the most 



