610 A TREATISE ON METAMORPHISM. 



tation, and from the silication of carbonates in the zone of anamorphism. 

 Therefore, the carbon dioxide for carbonation in the belt of cementation is 

 contributed by the belt of weathering above, by the zone of anamorphism 

 below, and by the belt of cementation itself. 



Bischof fully realized the very great abundance of carbonic acid in 

 "a numerous class of springs which are abundantly distributed over the 

 surface of the earth, especially in districts where extinct volcanoes or 

 basaltic rocks occur.'" 1 He also notes that "carbonated springs which 

 evolve abundance of this gas are likewise met with in the midst of sedi- 

 mentary formations.'"' The locations of a very large number of carbonated 

 springs scattered through extensive regions are mentioned." Bischof 

 further says that the carbonated springs "are always situated at the lower 

 part of mountain declivities or at the deepest points of valleys, gener- 

 ally near brooks;" while "fresh-water springs issue at points still higher 

 above the bottom of the valley, and sometimes at tolerably considerable 

 heights." d He further fully realized that the springs bringing the carbonic 

 acid abundantly to the surface are deep-seated waters which have arisen 

 from considerable depths. 6 Finally, Bischof attributes the abundance of 

 carbonic acid in the waters of deep ' springs and those which come from 

 deep borings to the silication of the carbonates. However, he recognizes 

 that the carbonic acid found in the waters of wells is also produced in part 

 by the oxidation of organic material/ Bischof therefore many years ago 

 correctly gave two main sources of carbon dioxide for the water of the 

 belt of cementation. 



It has been fully explained on pages 160-161 that, under the conditions 

 of the belt of cementation, where the rocks support themselves and open- 

 ings exist, the reactions take place which liberate heat. Carbonation of 

 the silicates and oxides belongs to this class. (See pp. 475-480.) It there- 

 fore follows from general reasoning that the carbon dioxide abundantly 

 supplied to the waters of the belt of cementation will react upon various 

 compounds and produce carbonates. Of the compounds upon which it acts 



a Bischof, Gustav, Elements of chemical and physical geology, trans, by Paul and Drummond, 

 Harrison & Sons, London, 1854, p. 217. 

 ''Bischof, cit., vol. 1, p. 217. 

 « Bischof, cit., vol. 1, pp. 218-241. 

 ''Bischof, cit., vol. 1, p. 223. 

 "Bischof, cit, vol. 1, pp. 228-230. 

 /Bischof, cit., vol. 1, p. 239. 



