Geological Gleanings. 26V 



changes effected by the eruption of 1852-53, one of the greatest 

 recorded in history. A brief account is given, extracted from 

 contemporary narratives and illustrated by a map, compiled with 

 the assistance of Dr. Giuseppe Gemmellaro, of the course taken in 

 1852-53 by various streams of lava, some of them six miles in 

 length, flowing during nine successive months from the head of 

 the Val del Bove to the suburbs of Zafarana and Milo. The pre- 

 sent aspect of this lava-field, parts of it still hot and emitting 

 vapour, and the numerous longitudinal ridges and furrows on its 

 surface are described. As to the origin of these superficial in- 

 equalities, the author inquires whether they may be due to the 

 flowing of lava in subterranean tunnels, or whether they be anti- 

 clinal and synclinal folds caused by fresh streams pouring over 

 preceding and half-consolidated ones, so that these last may be 

 bent and crumpled by the newly superimposed weight, like soft 

 yielding ground on which a railway embankment has been made. 

 The cascade of the lava of 1852, descending a precipitous declivity 

 500 feet high, called the Salto della Giumenta, and the stony cha- 

 racter of the layers which encrust the steep slope at angles of 

 more than 35° and even 45°, are commented upon. This lava 

 has overflowed that of 1819, which congealed on the same preci- 

 pice; and it is shown that in such cases the junction-lines separating 

 two successive currents must be obliterated, the bottom scoria? of 

 the newer dovetailing into the upper scoriae of the older current. 

 " The structure of the nucleus of Etna, as exhibited in sections 

 in the Val del Bove, is next treated of, and the doctrine of a 

 double axis is deduced from the varying dip of the beds. The 

 strata of trachyte and trachytic agglomerate in the Serra Giannicola 

 seen at the base of the lofty precipice at the head of the Val del 

 Bove are inclined at angles of 20° to 30° N. W i. e. towards the 

 present central axis of eruption. Other strata to the eastwards 

 (as in the hill of Zoccolaro) dip in an opposite direction, or S.E., 

 while, in a great part of the north and south escarpments of the 

 Val del Bove, the beds dip N.E. or N., and S.E. or S. respectively. 

 There is, therefore, a quaquaversal dip away from some point 

 situated in the centre of the area called the Piano di Trifoglietto. 

 Here a permanent axis of eruption may have existed for ages in 

 the earlier history of Etna, for which the name of the axis of Tri- 

 foglietto is proposed, while the modern centre of eruption, that 

 now in activity, may be called the axis of Mongibello. The two 

 axes, which are three miles distant the one from the other, are 



