Volcanoes. 



263 



eruption is not announced by any noise or dull murmur in the 

 interior of the mountain ; and it is always with surprise that 

 one sees the stones darted into the air. There are times when 

 the eruption is more precipitate and violent ; and stones de- 

 scribing more divergent rays are thrown into the sea at a 

 considerable distance/* 



It has been stated by Dolomieu, Hamilton, and Scrope, on 

 the authority of the islanders, that during the winter seasons 

 the eruptions are far more violent than in summer ; and that 

 from its appearance they can generally predict the changes in 

 the atmosphere. Sometimes during the storms of winter the 

 cone is split, and large currents of lava are discharged. 

 (A- 61.) 



Volcanoes are in the Phase of moderate Activity when they 

 are in a state of frequent and prolonged, but inconsiderable, 

 excitement. Under this class we may place the volcano of 

 Popocatepetl in Mexico, which was found in this phase by 

 the discoverers of the country. Such, also, was the condition 

 of Vesuvius from the commencement of this century to the 

 year 1822. 



The Phase of prolonged Intermittences is characterised by 

 lengthened periods of repose, and eruptions of the most vio- 

 lent description. It has been maintained by Baron Humboldt 

 that lofty volcanoes are always in this condition. The vol- 

 canic mountains of the Andes, for instance Cotopaxi and 

 other elevated craters, have not an eruption, generally speak- 

 ing, more than once in a century. The Peak of TenerifFe, 

 which was active in 1 798, had not at that time been disturbed 

 for ninety-two years. It must not, however, be supposed that 

 the phase of prolonged intermittences is confined to elevated 

 craters, for history gives abundant instances to the contrary. 



s 4) 



