958 The American Naturalist. [November, 



rographers, to the number of over fifty, was held, Zirkel presid- 

 ing. The discussions were animated, centering upon classifi- 

 cation, but resulted in the following almost unanimous expres- 

 sion of opinion, which was presented through the council to 

 the Congress: 



" It is not desirable, in view of the present rapid develop- 

 ment of the science of petrography, to attempt to establish 

 definite principles of classification of rocks by a resolution of 

 the Congress. 



" To attain the simplification of petrographic nomenclature 

 demanded by geologists, it is necessary to define with greater 

 precision than has yet been done such general terms as are 

 required in geological mapping." 



A resolution presented by Brogger expressed the view that 

 it was desirable and probably practical to establish a interna- 

 tional journal of petrography devoted chiefly to reviews and 

 abstracts of the current literature. This resolution excited 

 considerable debate, but was finally adopted and transmitted 

 to the Congress with the request that a committee be appointed 

 to ascertain the feasibility of the plan. The committee named 

 consists of fifteen men, the American members being Iddings 

 and Pirsson. 



Papers of interest presented in this department W'Cre by 

 Walter, Jena, Versuch einer Classification der Gesteine auf 

 Grund der vergleichenden Lithogenie, and by Loewinson-Les- 

 sing, Dorpat, Note sur la Classification et la Nomenclature des 

 Roches Eruptives. 



Walter attempts a general classification, his basis being the 

 recognition of primary and of secondary characters in rocks, 

 of which the first alone determines the place in the system. 

 Thus every metamorphic rock, however altered by " secondary 

 characters," is grouped under the rock from which it is derived. 

 He makes four main groups, Mechanical, Chemical, Organic 

 and Volcanic Rocks. 



Loewinson-Lessing bases his classification of the eruptive 

 rocks wholly on their chemical composition, expressed in terms 

 of the " oxygen equivalent," and of the ])roportions of the 

 various oxides. 



