

■'^ There 

 "^ tJie blaci 



''^o"^ sloping 

 ' ^e points 



'. andstict 



t he floatiij 



' ai of tk 



madrepores, 

 «nll oftener 

 ui-fke often 



,m of coral 

 ,1. 1 Iiad an 



could tear 

 (fhe stones 



it started a 

 nr ^vav^P 



} 



fas 



OV^'I^ 



A. 



re 



beic? 

 ei 





c 



ftl 



,1 tli^ 



-J 01 





J 

 1) 





Ch. XXVI.] ANCIENT LAVA CUERENTS CONFOEMAELE. 





>lf '^'^^^^ *liT^ them, to ascertain that they were not soldered on to tlie mass 



and althongh tlie day Avas clondj, tlie green turf 



of scoriae below; but I found tliem free to move and onlj 

 holding on by tlie slight inequalities of their surface. 



When at length we reached Finocchio we found it standing 

 like a rocky islet submerged up to its middle in lavas of 

 different ages^ and with the fresh current of 1852 near its 

 base. The relief afforded to the eye by that oasis was very 

 great ; 



enlivened by the flowers of a yellow ragwort^ looked dazzlino^ 

 by contrast with the dark surrounding desert, and the 

 autumnal crocus {colcJiicum autumnale)^ also in full bloom, 

 seemed more than ever beautiful. 



The manner in which pieces of loose scorise had often rolled 

 down in great numbers from the ridges into the troughs of 

 the lava serves to show to what an extent superficial inequa- 

 lities may be reduced, or even effaced, when fresh currents 

 overflow older ones. This may partly account for the regu- 

 larity and parallelism of the successive stony lavas with their 

 upper and under scoriae in the escarpments of the Val del 

 Bove ; but the chief reason why those ancient currents are 

 for the most part so conformable to each other is, I believe, 

 the steejpness of the slope down which they descended ; the 

 lofty and sharp ridges above described being characteristic of 

 lavas flowing on more level ground or down slightly inclined 

 planes. When they descend very steep slopes the very 

 moderate thickness which they attain is alone suflicient to 

 preclude the possible formation of undulations like those just 

 described, which are from 10 to 30 feet or more in height. 



Cascades of lava at Salto della Giumenta. — Some very 

 instructive examples are to be seen at various points on 

 Mount Etna of the external form and internal structure 

 assumed by currents of lava of known date which have flowed 

 down very steep slopes. To one of these, which was precipi- 

 tated in 1819 down a precipice which forms the head of the 

 valley of Calanna, allusion has already been made, page 29. 

 This precipice, called the Salto della Giumenta, is about 400 

 feet high and several hundred wide. In the annexed drawing, 

 fig. 85, which I made in 1828, it is seen in profile with a 

 branch of the lava of 1819 a, flowing over it. Fig. 86 is a front 



e 



VOL. II. 



D 



9 



