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: 
“Tt 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 Brégger 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 were 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 proportions of the 
various oxides. 
