856 THE JOURNAL OF GEOLOGY. 



Einleitung in die Geologie als historische Wissenscliaft. By Johannes 

 Walther. Jena, 1893-4. 



In this new work of Professor Walther the inductive method 

 receives a new and highly interesting treatment in its application to 

 historical geology. There are, we are told, four principal methods of 

 attacking the historical phases of geology, (1) the astrophysical method 

 which begins with the earth as star-dust and studies its development 

 from the speculative and mathematical standpoint of the astro- 

 physicist; (2) the tectonic method which studies the structure of the 

 crust and strives to reconstruct therefrom the changes which have 

 taken place in it; (3) the experimental method in which geological 

 phenomena are reproduced on a small scale in the laboratory ; (4) the 

 ontologic method. 



The experimental method can, evidently, but rarely become a dem- 

 onstration in the study of geologic phenomena, because we cannot 

 often reproduce all the natural conditions and we know that the same 

 results may often be produced by different methods. Thus coal may 

 be procured by the rubbing or pressure of wood or by its imperfect 

 combustion or by the action of acid upon cellulose tissue or by burn- 

 ing oil of turpentine. So also we may easily produce dolomite in the 

 laboratory but to produce it from limestone and sea-water, observing 

 the same conditions as those under which it is produced in nature has 

 been the object of a great deal of unsuccessful experimentation. In 

 many cases it is impossible for us to discover all the conditions under 

 which the natural phenomena occur. 



The experimental method must, therefore, be enlarged and at the 

 same time held in check and corrected by a fourth method, the onto- 

 logic method as it is here called. This method consists in a word in 

 making the earth our laboratory, in studying the processes by which 

 geological history is being made now, and in making this study the 

 point of departure for (introduction to) the study of historical geology. 

 "We determine the origin of dead volcanoes by studying the forma- 

 tion of those now building ; we form a basis for understanding the 

 history of a fossil coral reef by examining a living reef; and the depth 

 of water at which a fossil oyster bank was formed is approximated by 

 a determination of the depths at which the genus Ostrea is now found 

 living." (Introduction, p. xiii.) 



Before entering further into the application of this method we 



