214 On Earthquakes — their causes and effects. 



with amazing rapidity through a channel similar to those 

 described. 



The many remarkable eruptions of volcanoes are well 

 calculated to prove the agency of the ocean. The mud- 

 volcanoes of Macalouba in Sicily, Modena and Bologna in 

 Italy, and those of the Crimea, of Java, and Iceland, must 

 be caused by water, drawn from this source and ejected 

 with the soil, intimately mixing with it on their passage to 

 the summit of the crater. 



Eruptions have taken place of dust only. A most re- 

 markable one of this kind happened very recently, 1815, at 

 Tamboro, near Java, when such showers were thrown up as 

 to produce total darkness a great distance. It continued to 

 fall three hundred and thirty miles distant, for nearly a whole 

 day. This must have been the sudden extrication of a 

 slumbering mass which may have been accumulating for 

 years in the bosom of the mountain. 



The air-volcano of Cumacatar described by Humboldt 

 presents an anomaly, and is not easily accounted for, except 

 on the supposition that it may be an old volcano, so nearly 

 extinct as to have heat enough only to cause a continued 

 draft or current of air. 



Of the irregularity of eruptions of volcanoes and occur- 

 rences of earthquakes, we have many curious instances. An 

 ejection of ashes for a few minutes, is sometimes succeeded 

 fey a calm of ten years. In 1766 the city of Cumana was 

 entirely destroyed in a few minutes, and shocks were hourly 

 felt during a period of fourteen months. In 1692, Port- 

 Royal, Jamaica, was destroyed, and the inhabitants were 

 obliged to remain on board of vessels for two months, on 

 account of the continued concussions experienced there. In 

 this earthquake persons were swallowed up, and by another 

 effort of nature exhumed. Dr. J. W. Webster, in his descrip- 

 tion of St. Michael, informs us that thirty-one shocks were 

 felt in the city of Ponta Delgada, in the space of a few hours. 

 In some parts of the chain of the Andes, eruptions take 

 place regularly every thirty or forty years. 



It has been the anxious inquiry of many geologists, in 

 what formation do volcanoes exist ? is it necessary they 

 should be nourished by any particular stratum ? In answer 

 to these queries, it may be said that those persons who judge 

 from the exterior of a burning mountain, which may be por- 

 phyry or any transition or secondary rock, that it necessarily 



