OF ARTS AND SCIENCES. 337 



opposition to the commonly received opinion, that he died of 

 apoplexy, and not of suffocation. 



A discussion arising upon the nature of the effluvia, ashes, 

 (fcc, emitted by volcanoes, Dr. Hayes remarked, that erup- 

 tions were of a mixed character, distinguished by lava over- 

 flows, sublimations, and chloridic and aqueous exhalations in 

 some cases, while in others the presence of atmospheric air 

 and vapor of water in large quantity gave rise to sulphurous 

 acid fumes, and sulphydric gases, with sulphur depositions. 

 Regarding the account of the death of the elder Pliny as 

 remarkably explicit in details, he thought the statement 

 in relation to emission of sulphurous fumes at that time as in 

 accordance with present knowledge on this subject, and yet 

 as in no wise opposing the interesting view which has just 

 now been presented of the cause of his death. The abun- 

 dant source of sulphur fumes and sulphydric gases is the 

 solfa-taras, which, generally in action, exhibit during erup- 

 tions their highest activity ; and these existed then, and now 

 exist, in the low grounds in the vicinity of Vesuvius, chang- 

 ing their places as the decompositions on which they are de- 

 pendent proceed. Solfa-tara action can hardly be classed with 

 true volcanic action, although primarily dependent on it. It is 

 a slow combustion, taking place among the aggregates formed 

 at the time of previous volcanic action, requiring the presence 

 of water for continuing it. The earliest history of Vesuvius 

 presents it as a solfa-tara consuming the lava rocks of an ear- 

 lier period, and its cones of later dates have been craters of 

 elevation, subject to degradation, which has several times oc- 

 curred. Pliny, at the time of his death, was at Stabias, where 

 were hot volcanic waters along the shores, marking the points 

 of solfa-tara action. The sulphur of commerce is derived from 

 the deposits formed by solfa-taras, and its immense quantity 

 aftords some estimate of their extent and antiquity. 



Mr. Everett followed, illustrating the changes in locality of 

 the solfa-taras, from his own observations, after an interval of 

 a few years had elapsed. He also stated as his experience, 



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