INTRODUCTION, 



The ftudy of thofe fubterranean fires which 

 fjccafion fuch phenomena, and ftill more 



that 



nearly a league in length. This current, parallel to one 

 elder, and confifting in the like manner of feveral ftratu 

 of melted matter, formed a projc£i:ion, the bafis of which 

 was volcanic fand mixed witli a kind of iron drofs. 

 Eleven days after the arrival of the lava at the fea, a 

 folid cruft was formed at its furface, upon which it 

 was pofTtble to afcend to within fifteen paces of the 

 place from which it ifTued ; but, as the heat then be- 

 came infuppoTtable, the obfcrvcr called to mind the 

 tragical fate of Pliny, and reprefled his curlofity. One, 

 iiowc\*er, may venture, without any danger, to walk on 

 a torrent of flowing lava, if care be taken to examine 

 its cffeds* In flat places it foon cools at the fuper- 

 ficies, which then becomes hard like thick ice, whilft 

 the liquid matter may be f«cn through the crevices, 

 continuing its courfc in perfect freedom below i but, 

 fometimcs, meeting with obftaclcSi it flows back, breaks 

 the cruft, and covers it with frelh boiling lava. In 

 declivities, therefore, and fmuofitics, it is long in ac- 

 quiring a durable degree of foiidityi and this the 

 •oriou* ought to obfcrvc with attention, 



** On 



