298 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



sedimentary strata, facilitates the fracture.' 7 Moreover, in the chain of 

 the Southern Andes we find the volcano Tolima, 5,613 meters (34- miles) 

 in height and distant about 200 miles from the sea, which experienced 

 a great eruption on the 12th of March, 1595. But this maximum of 

 distauce of an active volcano upon the American continent is hardly the 

 tenth part of that at which we find in Central Asia the active volcanoes 

 of the chain of Thian-Chan, which, according to reliable information, 

 have emitted flames, lava, and pumice-stone since the first century of 

 our era. "The hesitation," says M. d'Archiac,* "to admit the existence 

 of these volcanoes because there are oil mines which, if on fire, would 

 present similar phenomena, is evidently forced, and rather a supposition 

 to sustain an hypothesis, which must, however, yield to facts which 

 cannot be doubted." 



This reflection applies especially to the partisans of the hypothesis of 

 Gay-Lussac, who are numerous and strong, on account of the facility 

 with which this theory is deduced from the two principal forces of the 

 earth, the sea and the central fire. As the hypothesis has its reason- 

 able side, we will give some of its principal features. 



At the commencement of this century it was considered that proxim- 

 ity to the sea was indispensable for the production of volcanic phenom- 

 ena. Examination of the products of the eruptions persuaded the 

 French chemist that they are the result of a reaction of the sea-water, 

 which penetrates through fissures to great depths, upon liquid and incan- 

 descent rocks, for the most part of silicates of potassium and aluminum. 

 In this case the different chlorides of the sea- water act upon the sili- 

 cates and produce by their decomposition, and a recomposition more in 

 accordance with their affinities, such an over-increase of heat that a vol- 

 atilization of the water, in spite of the enormous pressure, is the conse- 

 quence. The steam forces its way through the fractured crust, and 

 carries with it the substances melted by its passage, such as trachyte, 

 basalt, and, at the present period, lava. In more recent times an 

 attempt has been made to attach the hypothesis of Gay-Lussac to that 

 of Mr. Elie de Beaumont, who attributes volcanic eruptions to a kind of 

 effervescence which the gases contained in melted matter produce as soon 

 as the pressure of the crust is removed by its fracture. By virtue of this 

 effervescence, which causes the melted matter to rise wherever the pres- 

 sure is least, the sedimentary audp rimitive rocks are injected with in- 

 candescent masses, sometimes of considerable volume. It is then that 

 water is supposed to intervene in these passages of injection; it reacts 

 upon the incandescent rocks, and from this reaction results a volcanic 

 activity, less productive in the outflowing of lava, but not less formida- 

 ble on account of the volcanic storms it occasions. 



The mud-volcanoes are undoubtedly the last effort of volcanic activ- 

 ity. M. Hochstetter has shown! us that the former eruptions of the 



* Histoire des prog res de la yt'ologie, 1. 1, p. 181. 



\Die Vulkane Javas, Sitzungsberichte der Wiener AkacL, xxxvi, p. 128. 



