VOLCANO. 



it is important to confider whether volcanoes are accidental 

 appendages, or neceflary parts of the terreilrial fyftem, for 

 " were we," as Mr. Bakewell obferves in his Introduftion 

 to Geology, " to regard volcanic craters merely as the vents 

 for fubterranean fires, a further inquiry would arife refpeft- 

 ing the utility of thefe fires. We cannot fuppofe that the 

 interior motions of our planet are not direfted to fome defi- 

 nite purpofe, with the fame wifdom and defign which are dif- 

 played in the external univerfe. The craters of ancient vol- 

 canoes greatly exceed any that are now aftive ; and the 

 quantity of matter thrown out mud have been commenfu- 

 rate with the mighty openings through which it was ejefted. 

 Now thefe immenfe volcanoes, whofe craters are many fquare 

 leagues in extent, had doubtlefs an important office to per- 

 form in the economy of nature. It cannot, therefore, be 

 unreafonable to fuppofe that the earth itfelf contains the 

 gre?', laboratory and ftorchoufe, where the materials that 

 form its furface are prepared, and from whence they were 

 thrown up at different times, through thefe vaft openings, 

 either in the ftate of mud, or in chemical folution, or in the 

 form of lava, or in the comminuted ftate of powders or 

 fand. The only inftances we have at prefent of rock 

 formations are volcanic ; the vaft volcanoes in America 

 throw out torrents of mud, which form Itrata of fome 

 hundred fquare miles in extent, and of confiderable depth. 

 And according to Humboldt, the further we trace back the 

 ancient currents of lava, the greater fimilarity we find be- 

 tween them and thofe rocks, which are confidered as primi- 

 tive. Thefe primeval eruptions took place when our prefent 

 continents were covered by the fia or by large lakes, at the 

 bottom of which they probably fpread, and enveloped the 

 remains of animals or vegetables, which we find buried in 

 the different ftrata. Long intervals of rcpofe might allow 

 time for the growth of other tribes of animals, which were 

 buried in the matter of fuccceding eruptions. The internal 

 fire afting with greater or lefs force on the ftrata already 

 formed, might occafion thefe diflocations and contortions fo 

 frequently obferved in primary and fecondary rocks." This 

 view of the fubjeft is confiftent with that fyftem of geology 

 which fuppofes the exiftence of a central fire in the globe, 

 and it afligns to that fire its ufe in the vaft chemical labora- 

 tory of nature. The exiftence of numerous attivc or ex- 

 tinft volcanoes proves the exiftence of this fire, their con- 

 neftion leads us to infer the great depth at which it is placed, 

 and the produftion of new land offers no obfcure indication of 

 the final caufe. The caufes by which this fire is called into 

 greater aftivity at certain periods, will probably for ever re- 

 main unknown ; but it is important to keep in mind the efien- 

 tial difference between combnftion and ignition. A fubftance 

 may remain red-hot for ages without undergoing any change, 

 if it be deprived of air, or the prefence of other fubttances 

 with which it is difpofcd to combine ; but by conibuftion a 

 chemical change is produced. A mafs of melted iron or 

 lava, inclofed within the globe, might remain unchanged for 

 Sny conceivable time, if protcfted from air or water by a 

 folid cruft of the fame material ; and it is only on the con- 

 tact of othc-r fiibftances, permeating or breaking through 

 the cruft, that the common effefts of fire would be pro- 

 duced. 



Granting a fufficiont fin.al caufe for the exiftence of fire in 

 the earth, the fatt will not be more furprifing than the 

 cmifTion of light and heat from the lun : of the manner in 

 which eitlier are generated, we are profoundly ignorant, as 

 we are alfo of the nature and effence of heat itfelf. We are 

 equally ignorant refpcftiii.j the caufes which have increafed 

 or diminilhed the inlenfity of fubterranean fires at certain 

 periods, and direifted them to certain parts of the earth's 



furface. The variation of magnetic polarity may lead us 

 to mfer that there are regular proceffes taking place in the 

 earth ; and that it is not an inert mafs, but a well-conftruaed 

 machine,containing withm it the materials and the meansofits 

 future renovation, direfted by the fame wifdom which guides 

 Its path in the heavens, and circulates the fluids through all 

 the various forms of organic exiftence that inhabit its furface. 

 Whether a time may arrive when the central fire, encreafing 

 Its adivity, ftiall again reduce the prefent continents under 

 Its dominion, we have no natural means of afcertaining. 

 The ancient Stoics, and many of the oriental philofophers, 

 maintained the dodrine of the deftrudion and renovation of 

 the world by fire ; the facred writers not unfrequently refer 

 to the fame event, announcing a period when " the earth 

 ftiall be burned up, and the elements ftiall melt with fervent 

 heat." 



Dr. Hooke formerly had maintained, that all land was 

 raifed out of the fea by earthquakes ; and many modern philo- 

 fophers feem to admit his hypothefis, though not, perhaps, in 

 Its utmoft latitude. Von Troil ( Letters on Iceland, p. 222.) 

 IS of opinion tliat this ifland has been produced by volcanoes 

 in the courfe of feveral centuries. Dr. Forfter, in his Ob- 

 fervations made during a Voyage round the World, p. 15 1, 

 after giving an ingenious conjeiture concerning the origin of 

 all the tropical low ifles in the South Sea, affures us, that 

 of the higher ifles there iu hardly one of them which has not 

 ftrong veftiges of its having undergone fome violent altera- 

 tion by a volcano. Some of them have volcanoes ftill fub- 

 fifting ; others, among which are Otaheite and Huaheinc, 

 feem to have been elevated, in remote ages, from the bot- 

 tom of the fea by fubterraneous fires. Sir William HamiU 

 ton is confident, that the ifland of Ifchia, the whole bafis 

 of which is lava, rofe out of the fea in the fame manner as 

 fome of the Azores. 



Dr. Prieftley (Obf. on Air, vol. i. p. 263.) thinks it not 

 improbable that the volcanoes, with which there are evident 

 traces of almoft the whole furface of the earth having been 

 overfpread, may have been the origin of our atmofpherc, as 

 well as (according to the opinion of fame) of all the folid 

 land. The fuperfluous phlogifton of the air, in the ftate in 

 which it in"ues from volcanoes, may have been imbibed by 

 the waters of the fea, which it is probable covered the fur- 

 face of the earth, though part of it might have united with 

 the acid vapour exhaled from the fea, and by this union have 

 made a confideiable and valuable addition to the common 

 mafs of air ; and the remainder of this overcharge of phlo- 

 gifton may have been imbibed by plants as foon as the earth 

 was furnifhed with them. 



The beds of lava are deepoft and iiarrowell in the proxi- 

 mity of the crater, and broader and (hallower as they 

 are more diftant, unlefs fome valley intervenes ; fcorix 

 and aflies lie ftiil more diftant. From tliefe obfervations 

 extinguirtied volcanoes are traced. Many excellent in- 

 veftigations of this fort may be feen in M. Soulavie's Iliftory 

 of the South of France. For further information refpcA- 

 ing volcanoes we refer to ^TN A, Stromboli, Systems o/" 

 Geology, Vrauviu.s, and Vl'LCANO. 



Foknnic ProduSs — The fubftanccs thrown out of vol- 

 canoes, or found in the crater, are inflammable, f.diiie, me- 

 tallic, and earthy, without water, and may be claffed as aeri- 

 form, fluid, or folid. 



Atriform Fluids. — Steam, or vapour, is frequently emitted 

 in a qniefccnt ftate of the volcano, and is fuppofed to per- 

 form an important part during the moft violent eruptions. 

 Suipiiuretted liydrogen gas is thrown out in great abundance 

 from all volcanoes. Carbonic acid gas is emitted from fome 

 volcanoes in a quiclccnl ftate. Of the other gafcous i>r volatile 

 3 M : fubftanccs 



