386 WASHINGTON AND DAY VOLCANOES OF SOUTHERN ITALY 



acter. Here they are dry and do not form thick continuous beds, but 

 occur as narrow streaks along innumerable crevices in the ground, or else 

 delicate flat "rosettes" from 1 to 5 cm. in diameter and with concentric 

 series of petals (plate 22), or else tulip-like forms. 



A preliminary examination of these salts shows them to consist for tlie 

 most part of sulphates, chiefly of alumina and potash, with less soda and 

 ammonia and little lime and magnesia. Iron is present in all, even the 

 purest white specimens. With the exception of a few bright yellow syjeci- 

 mens, colored by ferric chloride, these deposits seem to be quite free from 

 clilorides, and lioric acid, while present in certain spots, does not seerf to 

 be as abundant as it was before the eruption. It appears that thiosul- 

 phates are present in the salts from inside the crater, wliile tliey are 

 absent from those on the crater slopes. These salts are now being investi- 

 gated chemically and optically.^^ 



The fumaroles proper were very active and numerous, occurring both 

 over the upper part of the cone and in the crater. The gases issue either 

 from beneath the large bombs which strew the rim and the inner slopes 

 of the crater or else from narrow, irregular holes in the ground. A small 

 group of tliese fumaroles is seen at the bottom of the crater, near the 

 north wall, and many of them (possibly fifty) are scattered over the inner 

 north and east slopes of the crater. There is also a "battery'" of them 

 issuing from the steep face of the tuff beds which form the inner wall of 

 the early crater on the south and soutliwest. On the Piano delle Fumarole 

 itself there are few or no fumaroles of this type at present except at the 

 west end of the terrace, above the upjier end of the Pietre Cotte, where 

 several occur. The most important and most active group is tliat just 

 below the east end of the Piano delle Fumarole, around the upper end of 

 the old conveyer cable, above the Forgia Vecchia, at an altiturle of 210 

 meters, shown in plate 23. 



These fumaroles give off a great deal of Avliite vapor — chiefly steam, 

 with much SO, and FI^S — which issues with considerable violence and a 

 loud hissing noise. Their temperatures generally varied from 99.0° to 

 10!)°, but that of the largest was US..1°. They do not deposit salts, but 

 an abundance of sulphur, in masses of transpnrent bright yellow acieular 

 crystals of the utmost delicacy, whicli are dewed with drops of water. 

 These crystals are of the moiioi-linic modification and on contact bi'eak 

 down to powder and lose theii' transparency through inversion to the 

 orthorhombic form. 



A characteristic of these fumaroles, as noted jjy de Fiore, is their ap- 

 parent permanency of location. Some of the larger ones antedate the 

 great eruption, and the largest, that at La Portella, shown in plate 23, is 



i^Cf. .T. Koenigsberger autl W. J. MiiUfr : ZeUs. Vulk., vol. i, 11U.5, p. ]9(;. 



