362 WHITMAN CROSS 
orders: (1) Alabradorites (rocks free from labradorite, gen- 
erally rich in quartz, and never containing augite); (2) Labra- 
dorites (rocks characterized by labradorite and free from quartz 
and orthoclase). These were subdivided into nine groups, 
according to the action of hydrochloric or sulphuric acid upon 
the rocks. For further details of this unique and highly 
artificial system the reader must be referred to the original 
work. 
J. Reinhard Blum, 1860.—Shortly after the treatises of 
Naumann, von Cotta, and Senft, there was published the Hand- 
buch der Lithologie oder Gesteinslehre, by J. Reinhard Blum.* This 
work is but little more than a descriptive handbook, with slight 
discussion of principles of classification, and in it no original 
contribution to the systematic science was made. The main 
divisions of the work are as follows: 
I. Crystalline rocks. 
A. Homogeneous. 
a, Granular. 
6. Schistose. 
c. Porphyritic. 
B. Heterogeneous —with three structural divisions, 
II. Clastie rocks. 
A. Cemented. 
B. Not cemented. 
The further division of crystalline rocks is by mineral com- 
position. 
Justus Roth, 7$6z.—Among the students of the chemical 
composition of igneous rocks none has rendered greater service 
than Justus Roth, who, in 1861, published his Geste:nsanalysen, in 
tabellarischer Ubersicht und mit kritischen Erlduterungen. Upon the 
basis of nearly a thousand analyses available at that time, Roth 
undertook to ascertain whether chemical composition gave in 
itself a practical ground for the classification of igneous rocks. 
As a basis for comparison of analyses Roth selected the oxygen 
ratio, 2. é¢., the ratio of the oxygen of the acid radical, SiO,, to 
that of the bases, RO (including R,O) and R,O,, and obtained 
* Erlangen, 1860, pp. 356. 
