038 



ELEVATION CRATERS NOT APPLICABLE 



[Ch. XXV. 



asked, can we reconcile with all these appearances the struc- 



mountain 



from the ravines 



above described, such as is revealed to us in the grand section 



of the Atrio ? 



may 



made 



ement and com 

 >v numerous dil 



to. 



modern 



thick, and consisting exclusively of fragmentary scoriae. In 

 many other cases the only part composed of solid rock is no 

 more than one or two feet thick, above and below which the 



mass 

 may 



Not 



Somma 



some oi • 

 3 modern 



some 



But the enquiry will still be made, how is it possible that 

 those continuous and horizontal sheets of stony lava, the edges 

 of which every observer recognises in the escarpment of 

 Somma, could have been formed by narrow rills of fluid matter 

 descending a slope of 20° ? The simple answer is, that there 

 are no such extensive stony beds. Signor Guiscardi and I 

 convinced ourselves, in 1858, that the supposed existence of 

 them is a delusion. There are 

 in particular, which is very conspicuous, which the eye traces 

 for a great length, in the middle of the great section, and 

 which, seen at the distance, have the character of stony layers. 

 They may have been produced simultaneously throughout 

 their whole extent in the same manner as some layers of 

 scorise of modern date, which have been seen to fall red-hot 

 from the air, and to cover the wide expanse of the mountain- 

 side with a mantle of fire. But when real sheets of stony 

 lava are examined, they are never seen to reach far in a hori- 

 zontal direction, but thin out, and pass laterally into scoria?. 







1' 





- 



Ka 



showers of ashes which in the years 1855 and 1857 have been 

 descending slopes of between 18 and 30 degrees, and forming 

 new envelopes of the cone arranged one above the other. 



In that part of the precipice exposed in the Atrio which 

 is called Canale del Inferno, flows of lava may be seen 12 feet .^lida I 



of the I 



lis mi 



d 





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ap wi . w 







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'bjace 





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md 



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