8 EXPLANATION OF PLATE I. 



Craters. 



Our section represents three cases of Volcanic craters ; 

 the most simple (i. 5.) rising through Granite, or stratified 

 rocks, at the bottom of the sea, and accumulating craters, 

 which, like those of Lipari and Stromboli, Sabrina, and 

 Graham Islands, are occasionally formed in various parts 

 of the ocean.* The second case is that of volcanos, 

 which, like Etna and Vesuvius, are still in action on the 

 dry land, (i. 1. to i. 4.) The third is that of extinct vol- 

 canos, like those in Auvergne, (h^ h~.) which, although 

 there exist no historical records as to the period of their 

 last eruptions, shew by the perfect condition of their cra- 

 ters, that they have been formed since the latest of those 

 aqueous inundations, that have affected the Basalts and 

 Tertiary strata, through which they have burst forth. 



One great difference between the more ancient Basaltic 

 eruptions and those of the Lava and Trachyte of existing 

 volcanos, is that the emission of the former, probably taking 

 place under the pressure of deep water, was not accompa- 

 nied by the formation of any permanent craters. 



In both cases, the fissures through some of which these 

 Eruptions may have issued, are abundantly apparent under 



the upward passage of the Lava through fractures in the solid 

 Granite. 



At Graveneire, near Clermont, a stream of Lava still retains the 

 exact form, in which it issued through a fissure in the side of a 

 mountain of Granite, and overflowed the subjacent valley. Most 

 accurate representations of this, and many similar productions of 

 Volcanic Eruptions from the Granite of this District may be seen in 

 Mr. Poulett Scrope's inimitable Panoramic Views of the Volcanic 

 formations of Central France. 



* Within the last few years, the Volcanic Cones of Sabrina in the 

 Atlantic, and of Graham Island in the Mediterranean, have risen 

 suddenly in the sea and been soon levelled and dispersed by the 

 Waves. 



