SIAS LEMWATH OC, SEVIS OX GIOIA al 6 365 
investigations which might show the feasibility of classifying all 
rocks in a similar manner. 
Upon scrutiny of his material and study of analyses of rocks 
from other localities, Scheerer was persuaded that all highly 
siliceous igneous rocks could be referred to the three magmas 
represented by the Saxon gneisses above mentioned, or to mix- 
tures of these magmas. The intermediate and basic rocks he 
believed could in a similar manner be assigned to six definite 
chemical types, and in the cited publication Scheerer outlined 
this chemical classification. 
Scheerer’s system expresses the idea that the molten material 
below the solid crust is arranged by specific gravity in zones, 
each of quite simple stoichiometric composition. He further 
believed that the upper, more siliceous magmas were first erupted, 
and the basic ones in late geological periods. From this cause 
the earliest rocks might be supposed to represent the funda- 
mental magmas more nearly than the basic ones, since the latter 
magmas must have passed through rocks of varied constitution 
in reaching the surface, and, therefore, suffered much modifica- 
tion through the fusion and assimilation of fragments torn loose 
in ascending. 
The nine chemical types of Scheerer were arranged in three 
groups, and named from rocks deemed to represent them in 
purest form. 
Oxvgen Ratio Oxygen Mean silica 
Si0g: RO+R203 (=1). Quotient. Percentage. 
PLUTONITES: 
Upper = “Rother Gneiss”...... 4.50 0.222 75 
Middle = “‘ Mittlerer Gneiss”’.... 3.75 0.267 70 
Lower = ‘‘Grauer Gneiss”...... 3.00 0.333 65 
PLUTO-VULCANITES: 
Upper = Quartz-bearing syenites. 2.07 0.375 63 
Middle Syemiter misc: citer clei 2.33 0.429 60 
ower—-Melaphiynemc sc ocsacis 2.00 0.500 55 
VULCANITES: 
Upper = Augite-porphyry...... 1.50 0.667 48 
Middle = Common basalt....... 1.33 0.750 42 
Lower = Basic basalt.......... 1.00 1.000 36 
