Ch. XV.] 



LAVA EXCAVATED BY THE SIMETO. 



357 



miles 



whole period which, has been sufficient for the hollowing out 

 of such enormous ravines. 



Recent excavation by the Simeto. — At the western base of 

 Etna, a current of lava (a a, fig. 21), descending from near 

 the summit of the great volcano, has flowed to the distance 



and then reached the alluvial plain of 

 the Simeto, the largest of the Sicilian rivers, which skirts 

 the base of Etna, and falls into the sea a few miles south of 

 Catania. The lava entered the river about three miles above 

 the town of Aderno, and not only occupied its channel for 

 some distance, but, crossing to the opposite side of the valley, 

 accumulated there in a rocky mass. Gemmellaro gives the 



Fig. 21. 



Eecent excavation of lava at the foot of Etna by the river Simeto. 



year 1603 as the date of the eruption."* The appearance of 

 the current clearly proves, that it is one of the most modern 

 of those of Etna ; for it has not been covered or crossed by 

 subsequent streams or ejections, and the olives which had 

 been planted on its surface were all of small size, when I 

 examined the spot in 1828, yet they were older than the 

 natural wood on the same lava. In the course, therefore, of 

 about two centuries, the Simeto has eroded a passage from 

 fifty to several hundred feet wide, and in some parts from 

 forty to fifty feet deep. 



The portion of lava cut through is in no part porous or 

 scoriaceous^ but consists of a compact homogeneous mass of 

 hard blue rock, somewhat inferior in weight to ordinary 

 basalt, and containing crystals of olivine and glassy felspar. 

 The general declivity of this part of the bed of the Simeto 

 is not considerable ; but, in consequence of the unequal waste 



* Quadro Istorico dell' Etna, 1824. 



