506 Geology and Magnetism. 



" That nearly all the substances which constitute the crust of the 

 globe are found in solution as well as solid, saturated throughout the 

 rocks, and to such a degree sometimes as to issue out and form 

 springs, is well known ; therefore, judging from the violent effects on 

 a small scale which we are able to produce by experiments, a heat 

 would be engendered quite adequate to occasion all that takes place 

 in volcanic eruptions. It is a fact, that nearly all active volcanic 

 groups are within a short distance of the sea ; and even those that 

 are situated at a distance from it may be connected with subterrane- 

 ous channels of water. It is also a well-known fact in South 

 America that fish are commonly thrown out of the crater, and some 

 of the eruptions consist entirely of mud or muddy water, thus giving 

 a still greater proof of their origin. The sudden fracture, as well 

 as the sudden expansion of the gases, would produce a vibratory 

 jar, which being propagated in undulations through the rocks or 

 external crust, would give rise to superficial oscillations, and thus 

 cause earthquakes. 



" We shall note here a singular fact connected with the earth- 

 quakes of South America, viz. during nine years' observations made 

 by the writer, the oscillations were from east to west, whilst the 

 directions of their disturbances, and the rumbling noise which 

 generally accompanies them, were from south to north. The former 

 were generally confined to comparatively narrow limits, whilst the 

 latter extended often from Chili to central America. 



" This meridional action of the subterranean currents from south 

 to north is not confined to South America, but extends to the 

 northern hemisphere. And it appears from numerous observations 

 made on the magnetic currents, that the power which governs 

 earthquakes and magnetic currents is the same. The mean direc- 

 tion of the latter in South America corresponds to the average 

 direction of the subterranean disturbances." 



We do not see that we can well curtail the following 

 remarks which constitute the 5th chapter of Mr. Hopkins' 

 work, which we give entire. 



"From a consideration of the general facts that have been stated 

 with respect to the effects of the galvanic current and its identity 



