356 



VOLCANIC ACTION. 



CHAPTER 

 XXVIII. 



MetalliferonB 

 deposits. 



clay, naptha, and irrespii-able gases. There is even an 

 obvious relation between the proper volcano and the for- 

 mation of beds of gypsum and anhydrous rock-salt, con- 

 taining petroleum, condensed hydrogen, sulphuret of iron, 

 and, occasionally, — as at Rio-Kualloga to the east of the 

 Peruvian coasts, — large masses of galena and sulphuret 

 Hot springs, of lead ; the origin of hot springs ; the arrangement of 

 metallic deposits ; earthquakes, which are ever and anon 

 accompanied by chemical phenomena : and the some- 

 times sudden, and the sometimes very slow, elevations of 

 certain parts of the earth's surface. It is during these 

 great changes in the earth's crust that the most of the 

 metalliferous deposits have occurred which now form so 

 valuable a source of economic wealth. The altered rock, 

 split into crevices, and, changed by the action of heat has 

 been anew filled up and agglomerated by the metals 

 forced upwards from nature's great laboratory into these 

 cracks which become the metalliferous veins. An intel- 

 ligent, scientific writer, in reviewing Baron Humboldt's 

 " Researclies in Central Asia," has remarked : — " The 

 study of these interesting phenomena, leads us to general 

 views of the catastrophes which have taken place in 

 times which preceded the historic era. The action of 

 the interior of a planet upon its outer crust, varies with 

 the stages of its progressive cooling, and with the inequa- 

 lities in the solidity and fluidity of the matters which 

 compose it. In our day this action is greatly enfeebled ; 

 it is confined to a small number of points. It is inter- 

 mittent, and less frequently displaced, and only produces 

 rocks, round small circular apertures, or longitudinal 

 crevices of small extent. It never exhibits its power 

 at gnat distances, excepting in shaking the crust of 

 the eartli in linear directions, or in circles of simultane- 

 ous oscillations, which continue the same for many 

 centuries. In these primeval ages, says Humboldt, 

 the elastic fluids or volcanic forces of our earth, more 

 energetic than at i)resciit, have made their way through 

 the oxidated and slightly solidified crust of our planet. 



General 

 views. 



Knfeebled 



volcanic 



actions. 



