^2S 6n Tii^ FORMATION OF ROCKS. [Augusf^ 



daily operation of the elements; but a field of Neptuni- 

 an rocks cannot be clianged into Volcanic but by fire. 

 The productions by fire are partial, violent, and at first 

 strongly markedj, but liaole to lose their characters hy 

 the daily and hourly operations of the elements. 



Mud Lava may perhaps be considered as the last 

 effbits of an expiring volcano, when the combustible 

 is nearly burned out, and the immense caverns, whence 

 w ere ejected the great currents of Lava, come to be filled 

 Vvith water, which gradually decomposing the bottoms 

 and sides turns them into clay and mud. 



The application of a sufficient quantity of heat to 

 the water in those caverns, so as to turn it into steam 

 t)Y elastic vapour, may perliaps be the most reasonable 

 manner of accounihig for these eruptions, which have 

 from time to time oveiTun whole countries 5 but the evi- 

 dence of their origin must rest either on tradition, or 

 the evidence of our senses ; for when once the circum- 

 stance of their being ejected from the boivels of the 

 mountain is forgo lien, there is no mark on the mud it- 

 self to distinguish it from mud deposited by a river j 

 tl'C sea) or any other aqueous agent. 



Cinders are a volcaiilc production that are ejected 

 fii all stages of the eruption, like showers, and fail on 

 the earth in strata of dliTerent colours, imitatiug the 

 fctratificatlon of Neptunian rocks, as at Oriot, in Spain; 

 hut when tb rovv 11 out in mass, and like a current, they 

 f,;e:]!crally indicate that the volcano is about to finish ; 

 fj.nfl t:mt the combustible pMi&r is acarly exhausted^:. 



