2O2 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



work accomplished now and in former epochs by the physical 

 and chemical agencies of subterranean water. 



Chemical Action of Water. The importance of water as a 

 chemical agent was early recognised, and its corrosive effects 

 on rocks were frequently discussed in the older literature. 

 K. G. Bischof 1 created a new scientific basis for this field of 

 geology. With admirable mastery of the subject, Bischof set 

 forth in his Text-book of Chemical and Physical Geology 

 (1846-47) all the chemical processes which take place when 

 meteoric water and different kinds of aqueous solutions come 

 in contact with rocks. He also enumerated and described the 

 minerals and rocks according to their chemical composition, 

 structure, texture, and characteristic modes of decomposition. 

 The new branch of geology thus outlined by Bischof attracted 

 great interest, and soon a large number of special memoirs 

 made their appearance. One of the best known works on 

 mineral decomposition was published in 1886 by Sterry 

 Hunt ; it treats for the most part the appearances of decay in 

 crystalline rocks. 



Evidences of meteoric weathering of the rocks are shown in 

 the changes of colour produced by oxidation, and in the 

 removal of the more soluble mineral constituents of rocks. 

 The superficial inequalities and degradation produced by sub- 

 aerial agents are enhanced by the percolation of water through 

 the body of the rock. Continued disintegration of the rocks 

 gives origin to soils and coarser debris, and the effect of dis- 

 integration may often extend to a considerable depth below 

 the surface, gradually' rotting and loosening a whole mass of 

 rock. The weathering caused by chemical changes alone 

 cannot, however, be regarded as a leading factor in producing 

 land-forms. Only the minor features of surface conformation 

 are due to the decay of rock in situ. The chemical and 

 mechanical forces of water must combine to produce the 

 major effects in surface conformation. The rapid removal of 

 decaying mineral matter by streams and rivers exposes fresh 

 rock surfaces to the disintegrating chemical action of the 



* Karl Gustav Bischof, born 1792 in Niirnberg, studied in Erlangen, and 

 was afterwards a university tutor there. In 1819 he. was made extra- 

 Ordinary Professor of Chemistry in Bonn; in 1822 he received. the full 

 professorship, and contributed in a high degree to the fame of that 

 university; died 3Oth November 1870 at Bonn. 



