16 



ETNA. 



[Ch. XXVI. 



Dihes in the Vol del Bove. — I have already alluded to a set 

 of dikes of greenstone or diorite, observed by Waltershauseu 

 to converge in the supposed centre of eruption or axis of 

 Trifofflietto (see p. 11). A 



much, greater number 

 Late from the modern 



eruption, or that of Mon 



They consist chiefly of 



dolerite or greystone, intermediate between trachyte and 

 basalt, — the trachi-dolerites of some geologists. They vary 



Fig. 77. 





Dikes at the base of the Serra del Solfizio, Etna, 



in, breadth from 2 to 20 feet and upwards, and usuall} 



project from 



face of tlie cliffs, as represented in tlie 



annexed drawing (fig. 77). They consist of harder materials 

 than the strata which they traverse, and therefore waste 

 away less rapidly under the influence of that repeated con- 

 gelation and thawing to which the rocks in this zone of 

 Etna are exposed. The dikes are, for the most part, vertical, 

 but sometimes they run in a tortuous course through tlie 

 tuffs and breccias, as represented in fig. 78. 



The dikes are most numerous near the head of the Val del 



C«' 



^ 



c^Vl-] 



to ,,upt) 



tiU 1^^'' . 



San &i^^ 



ence 



s 



recisely 



.lid roct w. 

 chaniiew 

 ssage 



Sot 



currents. 



blend 

 .•niination 



ter 



ntli eurrents ( 



tkt tky stof 



leir vertical ( 

 and do not ci 



were of a date 

 Weh 

 We been 



ow n 



per 



1 



^f perceive tl 

 ^tna liave air, 

 .S^eat liollow. 



'ig. the roc 



livi 



^"st iniicli of 1 

 *g up of 

 ^^ lias int 



^''' deluged 

 ''' now I'l- 



on 



one 



^^eli^ 



'T one 

 side 







K^ 



e 



5 Or 



a 



inen 



Will ; ^ ^1 



, ^oiisi. 



