Geological Obfervatlons. 393 



pudding-ftones are found, which have lava 

 for their ground. 



Bafaltes, and in many inftances fhoerl, feem 

 to me to ow6 their origin both to fire and 

 water : they feem to have been atfirft a lava, 

 but this lava, while in a liquid ftate being im- 

 merfed in water, was fo diffufed or diffolved 

 in it with the affiftance of heat, as to cryfta- 

 lize when cold, or coalefce into regular forms. 

 That bafaltes is not the refult of mere fufion 

 appears by a comparifon of its form with its 

 texture ; its form, it being cryftalized, fhould 

 be the effect of a thin fufion, but in thatcaie 

 its texture fhould be glafly; whereas it is 

 merely earthy and devoid of cavities. Hence 

 we may underftand how it comes to pafs that 

 lava perfectly vitrified, and even water, are 

 fometimes found inclofed in bafaltes. Mon. 

 Mineral. 511. Von Troi/, 285. 



The immenfe mafles of lava ejeded by 

 volcanos, prefenting but a relatively fmali 

 furface to the atmofphere, are many years in 

 cooling, and many hundreds of years are re- 

 quired for their decompofition ; this decom- 

 pofition is quicker or flower as they have been 

 more or lefs perfectly melted. According to 

 the obfervations of Sir William Hamilton, the 

 lava of Vefuvius forms one or two feet of 

 mould in 1000 years; this bed of mould 



being 



