Natural History of Volcanos and Earthquakes. 255 | 
the hot springs of Mariana and Las Trincheras rose severa) de- 
grees. According to the observations of Hamilton, Della Torre, 
Abbé Soulavie, Von Humboldt, and Forbes, the hot spring named 
La Pisciarella, which rises near Naples, from the exterior of the 
- cone of the Solfatara, is subject to extraordinary alternations in 
its temperature, from 101° F. to 199.°4 F.* But even in very 
short periods striking differences are sometimes found. Thus — 
Forstert asserts, that-in the neighborhood of Tanna, a voleano 
on one of the New Hebrides, the hot springs vary several degrees 
in temperature from one day to the other. : 
There is not, perhaps, a more striking example of intimate con- 
lection existing between volcanic phenomena and hot springs 
than in Iceland. As the volcanic eruptions are there confined to 
the district of the trachyte formation, so also are the principal 
mineral Springs only found in this formation ;{ from which it 
seems natural to infer, that it is one and the same process acting 
M both cases, but in a different manner.$ 
The hot springs in this voleanic island confirm Krug Von Nid- 
da’s system of classing thermal springs—namely, 1. such as are 
“nstanily bubbling and boiling up—permanent thermals ; 2. 
€ in which this ebullition only takes place at particular peri- 
ods, and which are perfectly tranquil during the remaining time 
—intermitting thermals ; and, 3. those whose surface ts always 
undisturbed, and in which no bubbling or boiling ever takes 
ée. The springs of the first class always have a temperature 
at the surface equal to that of boiling water under the usual at- 
Mospheric pressure. ‘Those of the second class only reach the 
boiling point during their temporary ebullition, and lose consid- 
erably in temperature during their period of rest. The springs of 
€ third class never reach the boiling point of water. 
The most famous of the intermittent springs is the Great Gey- 
Ser. At the time when Krug Von Nidda visited it, it presented 
tWo different kinds of eruption. The smaller ones were repeated 
tegularly every two hours; and the water was thrown only from 
teen to twenty feet high. 'The greater ones succeeded each 
# 
Forbes, loco cit. p. 611. t Journ. de Phys. 1779, p. 434. 
*Alll the hot springs of Mezico also rise out of trachyte and dolerite rocks. Burk- 
“th, p. 363, 
t § Krug Von Nidda on the mineral springs of Iceland, p. 272, in Karsten’s Archiv. 
%; P- 247, and in Jameson's Phil. Jour. vol. xxii, p. 90 and 220, 
