1858.] 



ABICH ^ETNA. 



121 



I found the same beds of lava laid open to the sight in the interior 

 of the neighbouring CistereUa. These beds rise in the vicinity of 

 the Montagnuola, and suddenly appear lifted up in order to form 

 the crater-like wall (fig. 5 a) which half surrounds the cone of the 

 Montagnuola, comparable (geologically) to Somma with regard to 

 Vesuvius, the central cone of eruption (c). 



All those lava-currents which the subsidence of the CistereUa cut 

 through, following the same iaclination as the Piano del Lago in its 

 beginning from the Torre del Filosofo to the Montagnuola, show a 

 peculiar resemblance to the modem currents of Etna, partaking 

 of the magnetic property in a very high degree. By this quality all 

 those superior lavas of the Piano del Lago, as well as the upper beds 

 of the Cima della Yalle on the northern side, differ essentially from 

 the older beds, of more trachytic composition, which form the veri- 

 table central body of the mountain. I may remark that I made a 

 similar observation with regard to the very notable petrographical 

 difference between the older rocks of Ararat and the black doleritic 

 lavas covering the upper part of the burst mountain. I believe these 

 physical differences of the rocks belonging to one and the same 

 system to be in intimate dependence on a notable change in the 

 mode of formation governing the whole system. 



Fig. 6. — Beds and DyTces on the slope between Giannicola atid 



Musarra. 



Direction of Dykes N.N.E.— S.S.W. 



^^'yptti 



'^^ylffy'r^'^ 



Fig. 6 gives an exact representation of what I saw higher up 

 than the great masses of the Giannicola or Musarra, illustrating the 

 almost horizontal position of the slightly curved beds, intersected by 

 dykes running in the above-mentioned direction of N.N.E.-S.S.W. 

 It must not be forgotten that this part of the slope corresponds to 

 the middle region of the interior body of the mountain (fig. 4 a, 6, 

 and fig. 1 CI), and that, in my opinion, both to the left and right of 

 those regions, the effect of original subsidence was still sensible 

 enough to prescribe the way that aU the future currents of doleritic 

 lava, poured out from the modem excentric volcano, should take down 

 to the vaUey. Putting aside my belief of the probability of all those 



