THE RELATIONS EXISTING BETWEEN PETROGRAPHY 

 AND ITS RELATED SCIENCES 



BY FERDINAND ZIRKEL 

 (Translated from the German by Cleveland Abbe, Jr., Washington, D. C.) 



[Ferdinand Zirkel, Ordinary Professor of Mineralogy and Geology in the University 

 of Leipsic, Director of the Mineralogical Museum and Institute, b. May 20, 

 1838, Bonn-on-the-Rhine, Germany. Ph.D. University of Bonn, 1861. Royal 

 Privy Councilor; Professor, University of Lemberg, 1863-68; Kiel, 1868-70; 

 Leipsic, since 1870. Member of the Academies of Science of Berlin, Vienna, 

 Munich, Gottingen, Turin, Rome, Christiania, New York; Royal Society, Lon- 

 don; Honorary Member, Royal Society, Edinburgh.] 



FEW other sciences have undergone such profound changes during 

 the last third of the past century as has the science of petrography. 

 The refined methods of investigation, especially the preparation of 

 thin rock sections, the employment of the microscope, and the appli- 

 cation of other optical instruments, to which are due in part the pre- 

 sent status of the science, have been invented, improved, and made 

 to bear fruit only within the past thirty or forty years. The resultant 

 increase in number of known facts and their correlation by means of 

 geological observations has been accompanied by increased efforts 

 to deepen our insight into the causal connections and genetic relations 

 between petrographic phenomena. During the same period there has 

 been also a rapid increase in the number of investigators along petro- 

 graphic lines. This increase is due in part to the inspiration and sup- 

 port of petrographic laboratories established during this period of 

 time, and in part to the national geological surveys whose collections 

 and activities have immeasurably increased the amount of study 

 material. Petrographical literature, previously limited almost wholly 

 to Germany, England, France, and Scandinavia, has also taken on a 

 much broader international character. A number of excellent young 

 students from the United States, after receiving training and inspira- 

 tion by several years of European study, have returned to their native 

 land, and by original independent research won for her a place in the 

 front rank. 



No science can exist wholly for itself alone, exerting neither a pass- 

 ive nor an active influence. Each science must make some use of the 

 results acquired by allied branches of knowledge for the furthering of 

 its own advancement, and again each must contribute from its own 

 results toward the advancement of other sciences. Since the science 

 of petrography deals with the materials composing the firm external 

 crusts of the earth, i. e., the rocks, there can be no doubt that the 

 sciences most nearly related to it are mineralogy, geology, physics, and 

 chemistry. These sciences, which enter most directly into the service 



