October 6, 1892] 



NATURE 



545 



little fissures in the ground in a direction approximately '• 

 parallel to that of the main rift. These, often over a 

 metre in breadth, are choked by the loose materials form- 

 ing the surface, and in part obstructed by the loose 

 materials forming their sides. Higher up we found a 

 wide cleft, which, starting from a higher point, was pro- ' 

 longed downwards towards the craters and was lost I 

 beneath the lava. Upon this fissure were arranged a series ^ 

 of crateriform elevations, some of which were extinct, j 

 and others still presenting a little solfataric action. On 

 July 9, at the commencement of the eruption, lava and 

 fragmentary ejecta also issued by this cleft, but it 

 seems, the same day, to have become obstructed, and the 

 tongue of lava which menaced the Casa del Bosco 

 stopped, and the eruptive phenomena were diverted to 

 the other more eastern fissure. 



It is absolutely impossible to accept the statement that 

 this cleft represents the fire vents of the eruption of 1766, 



re-ejected, or are pieces of rock detached from the walls 

 of the volcanic chimney. Certainly from the last source 

 are derived quartzites, which we collected amongst the 

 ejected materials from this crater. This quartziteis semi- 

 vitreous, very similar to that which we collected from the 

 craters of the eruptions of 1883 and 1886. These facts 

 evidently showed that all these three eruptions have tra- 

 versed similar strata and that all have arisen over 

 the same principal cleft. In fact the new eruptive 

 apparatus formed at the base of the Montagnola about 

 1900 m. above sea level, lies on the northern prolonga- 

 tion of the rift of 1886, in a plain gently inclined toward 

 the south, and which towards the east presents a marked 

 slope, so that the new craters are much higher on their 

 eastern side. In the great paroxysmal eruptions, and 

 when a large rift opens at the surface of the earth, it is 

 generally the rule that the eruptive mouth from which 

 the lava flows without much explosive force is situated 



-Taken by Sig. Modu on July 13, 



2, at 150 m. to the north- weit of the craters. Craters No. i and 2. («) Monte Nero. 

 (/«) Little northern crater. 



and that the solfataric phenomena which the cleft now 

 exhibits are only due to the near vicinity of the new vol- 

 canic outlet, for— putting aside the fact that in visits ante- 

 rior to the present eruption I had never found any sign of 

 such, and this is confirmed by people accustomed to the 

 locality — it is easy also to be convinced from the 

 nature of the materials composing these craterets. These 

 materials are so new as to leave no doubt as to their 

 origin, and consist, those higher up, specially of blocks 

 of old lava torn from the sides of the cleft ; lower down 

 they are principally scoria and other loose materials of 

 irecent formation. 



Approaching still nearer, we were able to distinguish 

 •clearly that amongst the ejected materials of No. i, be- 

 sides the number of fragments of molten lava, there are 

 often blocks ofa dark grey colour that were already con- 

 solidated before their final ejection, which are either pro- 

 jectiles that have fallen back in the crater and have been 



NO. 1 I 97, VOL. 46] 



at its lowest extremity. The higher one goes along the 

 fissure the less is the amount of lava that issues, but the 

 greater is the explosive action, which higher still itself 

 in turn diminishes. In the present eruption we have 

 good examples of this. In fact, the small northern crater 

 gave forth only dust, and very few fragments of new lava, 

 and with little energy. No. i crater emitted much dust and 

 also much lava ; No. 2 more lava than dust, and Nos. 3 

 and 4 exclusively lava. The materials of the little north- 

 ern crater (Fig. 3) are for the most part fragments of 

 ancient lava, which lose their predominance in crater 

 No. I, and gradually disappear as one descends lower 

 and lower. At the same time, as the old lava has a light 

 bluish-grey colour and the fragments of the newer lava 

 are much darker, the diflferent craters exhibit different 

 colours. This difference also depends in part upon the 

 degree of fineness of the materials that compose the 

 craters. In fact the northernmost crater at the beginning 



