262 



CRATERS OF ERUPTION AND ELEVATION. 



hot cinders and dust were quickly succeeding each other, while 

 forked lightning, accompanied by rattling thunder, darted from ail 

 directions within the column now darkened with dust, greatly in- 

 creased in volume, and distorted by sudden gusts and whirlwinds." 

 The latitude of this island is, or rather was, 37° 11' north, and lon- 

 gitude east 12° 44'. 



At the beginning of January in the following year, the top of the 

 island was somewhat below the surface of the sea, and at the latter 

 end of February, soundings had been made at different times, which 

 discovered depths of from fifty to one hundred and fifty feet, from 

 the surface of the sea to the cone of the volcano. This sudden 

 sinking down of the volcano must be attributed to the subsidence of 

 the ground beneath it. 



' The French geologists who visited this submarine volcano describe 

 the island as being a crater of eruption [cratere d'^eruption), while 

 the base below the sea is supposed to have been formed by the up- 

 heaving of solid rocks, or to be a crater of elevation {cratcre de 

 soulevement.) 



Craters of eruption are formed by the accumulation of lava or 

 other volcanic matter around the orifice from whence they flowed, 

 or were projected. Such is, perhaps, the origin of the greater num- 

 ber of volcanic craters. That eminent geologist, Von Buch, how- 

 ever, maintains, that beds of primary, or other rocks, have been 

 sometimes raised from beneath the sea to considerable elevations, be- 

 fore the subterranean fire had opened a passage for the eruption of 

 lava or scoriae. Suppose successive beds of lava to have been pour- 

 ed through a chasm over the bottom of the ocean, and afterwards 

 consolidated, and the chasm to become covered by an immense 

 mass of solid lava ; in a succeeding paroxysm, the volcanic energy 

 being unable to force a passage through the former opening, and 

 thus acting with compressed intensity, might upheave the beds of 

 submarine lava and the subjacent rocks to a considerable height 

 above the sea, before a new passage was -opened for a subsequent 

 eruption. This would be a crater of elevation. With the ancient 

 lava, the lower beds of granite or other rocks might also be raised up. 

 This mode of volcanic operation is so analogous to that which has 

 up-heaved mountain masses in every part of the globe, that I am at 

 a loss to conjecture on what principle it has been objected to. Let 

 the reader refer to the position of the beds at Wren's Nest Hill, near 

 Dudley, and their continguity to basalt (Plate III. fig. 4.) ; or, what 

 may be more directly to the purpose, let him turn to the section ~ 

 of Crich Cliff (page 95.), in which the strata encircle and cover 

 the hill, like the coats of an onion, and in which there is a rnass of toad- 

 stone near the centre. Few geologists will deny that the beds have 

 been up-heaved by a power acting from beneath ; or that the protru- 

 sion of beds of volcanic toadstone was the original cause of the ele- 

 vation of the strata. If the up-heaving power at Crich Cliff had 



