GROWTH OF GEOLOGY. 275 



position and crystalline form, both he and Berzelius 

 went too far in declaring similarity of crystalline 

 form to be " a mechanical consequence of similarity 

 in atomic constitution," or in other words that the 

 atomic constitution of a substance could be inferred 

 if that of one of its isomorphs was known. For 

 Mitscherlich afterwards showed that dissimilarly 

 constituted bodies might be isomorphous and simi- 

 larly constituted ones heteromorphous, and that the 

 same substance might crystallise in different forms. 

 To this Scherer added " cases of the so-called poly- 

 meric isomorphism, which proved that elementary 

 atoms might be replaced by atomic groups without 

 change of crystalline form." * 



Experimental. We have already referred to Sir 

 James Hall as the founder of experimental geology, 

 and may here recall that in 1801 he showed the possi- 

 ble transformation of chalk into marble. For this 

 was as it were the first sentence in an exceedingly 

 interesting chapter in the history of research the 

 development of experimental mineralogy. Numer- 

 ous experimenters particularly well represented in 

 France e.g., in modern times, Fouque and Michel- 

 Levy, Friedel and Sarasin have worked at the arti- 

 ficial production of minerals, and have thrown much 

 light upon the possible ways in which minerals may 

 have been formed in nature. 



NOTE OX THE SCIENTIFIC DEVELOPMENT OF 

 GEOGRAPHY. 



One of the great intellectual advances of the nine- 

 teenth century has been the scientific development 

 of geography. Whether we recognize one science or 



*E. von Meyer. History of Chemistry, Trans. 1891, p. 

 454. 



