42 WASTE AND RECONSTRUCTION. 



stiller waters, or strewn along the courses of the ocean-cur- 

 rents in long reaches of miscellaneous debris, partly of ani- 

 mal, partly of vegetable, and partly of mineral origin. The 

 effect of aqueous agency is thus partly to wear and waste, 

 and partly to accumulate and reconstruct to wear down 

 the old continents and to accumulate the abraded materials 

 in the waters for the formation of newer lands. 



The Chemical agencies, though less perceptible, are not 

 less general or less incessant in their action than the mete- 

 oric or aqueous. Indeed, in a certain sense the meteoric 

 and aqueous act chemically but we have hitherto alluded 

 chiefly to their mechanical effects, and now direct attention 

 more especially to their chemical. The carbonic acid of 

 the atmosphere eats into the most crystalline marble ; its 

 oxygen converts the hardest ironstone into a soft earthy 

 peroxide, ready to be washed away by the first shower that 

 falls. Every spring that issues from the interior of the 

 earth holds in solution, less or more, some mineral or 

 metallic matter, which it either deposits along its course or 

 carries forward through stream and river to the ocean. Be 

 it lime, or iron, or flint, or salt and such matters constitute 

 our petrifying, chalybeate, siliceous, and saline springs 

 these matters must have been dissolved or wasted from the 

 interior, as they are now brought to its surface to form new 

 rock-masses or to enter into newer combinations in the 

 waters of the ocean. And this chemical effect of springs is 

 vastly increased when the waters are hot, whether bursting 

 forth like the Geysers of Iceland, or simmering like the mud 

 and sulphur vents that appear in the neighbourhood * of 

 almost every active volcano. Heat, indeed, is the great 

 promoter of chemical change within the earth's crust ; and 

 from this cause arise, no doubt, those discharges of naphtha, 

 petroleum, and the like, that result from the slow decom- 

 position of lignites, coals, and other organic masses. It is 



