Natural History of Volcanos and Earthquakes. 255 



the hot springs of Mariana and Las Trinclieras rose several de- 

 grees. According to the observations of Hamilton, Delia Torre, 

 Abbe Soulavie, Von Humboldt, and Forbes, the hot spring named 

 La Pisciarclla, 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 

 Forsterf asserts, that in the neighborhood of Tanna, a volcano 

 on one of the Neio 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- 

 nection 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 

 in both cases, but in a different manner.<§) 



The hot springs in this volcanic island confirm Krug Yon Nid- 

 da's system of classing thermal springs — namely, 1. such as are 

 constantly huhbling and boiling up — permanent thermals ; 2. 

 those in which this ebullition only takes place at particular peri- 

 ods, and which are perfectly tranquil during the rentaijiing time 

 ' — intermitting thermals ; and, 3. those whose surface is ahvays 

 undisturbed, and in lohich no babbling or boiling ever takes 

 place. 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 

 boihng point during their temporary ebullition, and lose consid- 

 erably in temperature during their period of rest. The springs of 

 the 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 

 regularly every two hours ; and the water was thrown only from 

 fifteen to twenty feet high. The greater ones succeeded each 



* Forbes, loco cit. p. 611. t Journ. de Phj's. 1779, p. 434. 



X All the hot springs of ./Ifexico also rise out of tracliyle and dolerite rocks. Burk- 

 art, p. 363. 



§ Krug Von Nidda on the mineral springs o? Iceland, p. 272, in Karsten's Arcliiv. 

 t. ix, p. 247, and in Jameson's Phil. Jour. vol. x.xii, p. 90 and 220. 



