Vol. 60.] VOLCANIC ACTION IN THE PHLEGR.EAN FIELDS. 311 



perhaps anterior in date to those of Astroni. Whereas, however, 

 the great cone of Astroni was thrown up, as it were, with one 

 spurt and finished off in a single gigantic though brief spasm of 

 eruptivity, followed by a few ejections of ashes and scoriae, and by 

 one scanty outflow of lava in the central portion of the crater : 

 the volcano of Solfatara, on the other hand, remained active 

 throughout a long period, giving rise to small outbursts of lava 

 within the crater itself, and to great trachytic flows which coursed 

 down its southern flanks as far as the sea, there forming the 

 Monte Olibano. In the Middle Ages incandescent lava was still 

 to be seen in the crater of Solfatara, and even at the present day 

 its temperature is higher than that of any other eruptive vent in 

 the Phlegraean Fields. To this long continuance is due the intense 

 alteration, which the gases customarily occurring in fumaroles have 

 induced in the materials of which the volcano is built up, in such 

 wise that it forms an unique instance in the Phlegraean area. The 

 very persistence of this activity, primarily eruptive and subsequently 

 solfataric, leads to the inference that a local magmatic basin, larger 

 than those of the neighbouring vents, exists beneath the Solfatara. 

 This supposition is confirmed by the relatively-greater quantity 

 of lava ejected from this vent than that poured out from the 

 other volcanoes of the Phlegraean Fields, which are, indeed, pre- 

 dominantly built up of fragmental materials. Generally speaking, 

 volcanoes of detritic or of tufaceous type represent the 

 outcome of rapid and violent explosive action, and hence 

 they have a much shorter life than volcanoes of the type which is 

 mainly lavaform or mixed. 



On the external north-western slopes of the great crater of 

 Astroni two small adventitious or parasitic volcanoes are to be seen : 

 Cigliano and Campana. The first-named is a simple cone, 

 with a crater eroded on the south by the action of winds and rains 

 upon the friable material of which the cone is wholly built up (ashes 

 and small pumice). The volcano of Campana, on the other hand, 

 belongs to the concentric type (vulcano a recinto), being made 

 up of three practically-concentric rings, within the innermost of which 

 is a small but most beautiful crater, rent on the east by a deep and 

 narrow fissure known as La Senga. These three 'girdle-craters' 

 of Campana consist of but little ash and lapilli, with a vast mass of 

 scoriae and bombs, red and black, of trachy-andesitic character, and 

 increasing in quantity inwards in such wise that the latest crater, 

 called the Fossa Lupara, may be said to be entirely composed 

 of blocks of lava. It seems probable that the rending-open of the 

 fissure of La Senga was brought about by the settling-down and 

 cooling of these blocks. 



Of practically the same type as Cigliano, that is, almost wholly 

 built up of ashes and pumice, with a few infrequent scoriae, is a tiny, 

 barely perceptible vulcanetto, known as Santa Teresa, which 

 lies on the plain of Bagnoli, south-east of the outer slopes of Agnano. 

 Here, too, as on Cigliano, the rain-laden southerlv winds have 



