60 Prof. Bischof on the Natural History of 



are seen to open, new springs to rise, and old ones to close. The 

 only difference is, that, as these changes are not accompanied 

 with any violent action, as is the case with volcanos, they re- 

 quire a greater length of time for their accomplishment. 



We have, in the preceding inquiries, as yet only supposed 

 the admission of water from the sea. But this does not seem 

 always to be the case, even in volcanos situated near the sea. 

 According to Hamilton,* the water of the springs and wells of 

 Torre del Greco diminished so much a few days before the 

 great eruption of Vesuvius, on the 15th June 1794, that the 

 eorn-mills at the principal spring were nearly stopped, and it 

 was daily necessary to lengthen the ropes in the wells, in order 

 to reach the water. Some wells dried quite up^ and on the 

 morning of the IStli June, at Resiria, a subterranean rumbling 

 noise was heard after a heavy rain. Monticelli and Covelli f 

 relate that, before the great eruption of this volcano in 1822, 

 at the beginning of January, the springs at Resina, St Jorio, 

 and particularly in the places in the immediate vicinity of 

 Vesuvius, diminished perceptibly. J Monticelli observed simi- 

 lar phenomena before the eruption in 1813, and he thinks 

 that, in general, they are a sure sign of one. It is hardly to be 

 doubted that rents were opened by the earthquakes, through 

 which the water descended to greater depths, accumulating, 

 perhaps, in great caverns, and from thence found its way to 

 the source of the volcanic action. 



We find considerable accumulations of water in all moun- 

 tains traversed by numerous fissures. We will only now men- 



* Phil. Trans, for 1795, p. 73. 



t Loco cit. pp. 12 and C3. See also Monticelli, in Leonard's Taschcn- 

 buch fiir die gesammte Mineralogie, vol. xiv. p. 87. 



J The same was observed twenty-three days before the earthquake in 

 ■Ciilahria; and. also in the Peak of Teneriffe, in 1706. Yon Humboldt, Relat. 

 Hist. t. i. p. 393. In Iceland^ this phenomenon was observed before the ter- 

 rible eruption of Slcajytar Jokul, in 1784. In general, in volcanic districts, 

 the porous and much fissured rocks swallow up the rain-water, and carry it 

 down to very great depths. Von Humboldt gives this as the cause of the 

 extreme aridity Avhich reigns in most of the Canary Islands, notwithstand- 

 ing the height of the mountains, and the mass of clouds which travellers 

 always see collected over this Archipelago. Reise, t. i. p. 173. 



