( 2IO ) 



What concKifion, then, ought we tode- 

 duce from all thefe facts and obfervations ? 



FirR : that many bafaltiform lavas have 

 aflumed this organization on coagulating 

 within the fea. 



Secondly : that others have taken the 

 fame form, merely in cooling in the open 

 air. 



Thirdly : that Innumerable other lavas 

 have not taken this figure, either in the fe:i 

 or in the air. 



It appears, at firft view, that thefe dif- 

 ferences depend on the different nature 

 of the lavas themfelves. This opinion, 

 at leaft, is rendered probable by what we 

 obferve in earths penetrated with water, 

 which, in drying, take, more or lefs, 

 prifmatic forms, as has been obferved fre- 

 quently in the argillaceous kinds. I have 

 feen, when a turbid torrent has been in- 

 troduced into a ditch through an argilla- 

 ceous marie, the latter, in drying, divide 



into 



