182 COSMOS. 



exactly analogous but far grander phenomenon, on the ash- 

 cone of the volcano of Sangai, which rises to a height of 

 17,006 feet to the south-east of the city of Quito, no trem- 

 bling of the earth 28 was felt by a very distinguished observer, 

 M. Wisse, when (in December, 1849,) he approached within 

 a thousand feet of the summit and crater, although no less 

 than 267 explosions (eruptions of cinders) were counted in 

 an hour. 



A second, and infinitely more important kind of earth- 

 quake, is the very frequent one which usually accompanies 

 or precedes great eruptions of volcanoes, whether the vol- 

 canoes, like ours in Europe, pour forth streams of lava ; or 

 like Cotopaxi, Pichincha, and Tunguragua of the Andes 

 only throw out calcined masses, ashes and vapours. For 

 earthquakes of this kind the volcanoes are especially to be 

 regarded as safety valves, as indicated even by Strabo's ex- 

 pression concerning the fissure pouring out lava near Lelante 

 in Eubcea. The earthquakes cease, when the great eruption 

 has taken place. 



Most widely 29 distributed, however, are the ravages of the 

 waves of commotion which pass sometimes through completely 

 non-trachytic, non-volcanic countries and sometimes through 



28 The explosions of the Sangai, or Volcan de Macas, took place on 

 an average every 13". 4, see Wisse, Comptes rendus de I'Acad. des 

 Sciences, tome xxxvi, 1853, p. 720. As an example of commotions con- 

 fined within the narrowest limits, I might also have cited the report of 

 Count "Larderel upon the lagoons in Tuscany. The vapours containing 

 boron or boracic acid give notice of their existence and of their ap- 

 proaching eruption at fissures by shaking the surrounding rocks (Lar- 

 derel, Sur les etablissements industries de la production d'acide boracique 

 en Toscane, 1852, p. 15). 



29 I am glad that I am able to cite an important authority in confir- 

 mation of the views that I have endeavoured to develope in the text. 

 " In the Andes the oscillation of the soil, due to a volcanic eruption, 

 is, so to speak, local, whilst an earthquake, which, at all events in ap- 

 pearance, is not connected with any volcanic eruption, is propagated to 

 incredible distances. In this case it has been remarked that the 

 shocks followed in preference the direction of the chains of mountains, 

 and were principally felt in Alpine districts. The frequency of the 

 movements in the soil of the Andes, and the little coincidence observed 

 between these movements and volcanic eruptions, must necessarily lead 

 us to suppose that in most cases they are occasioned by a cause inde- 

 pendent of volcanoes" (Boussingault, Annales de Chimie et de Physique, 

 t. Iviii, 1835, p. 83). 



