S4SIPEIA THE IVE INS OUG al) Z 337 
was warmly advocated on the one hand, and as fervently 
denounced on the other. 
Development of mineralogy.— The latter half of the eighteenth 
century witnessed great advances in knowledge concerning the 
materials of the earth’s crust, and toward its close there began 
to crystallize out of that knowledge the three sciences of min- 
eralogy, geognosy, and petrography, although the latter was 
long unnamed. 
With more and more accurate information as to the constant 
chemical composition of minerals, and under the influence of 
Haiiy’s brilliant conception of molecular structure and crystal 
form as attributes of these substances, mineralogy rapidly 
advanced to its place as a definite branch of science. Its subject- 
matter grew more and more homogeneous by a process of exclu- 
sion, as it became clear that many composite or impure substances 
had been erroneously classified with minerals. But the mineralo- 
gist of this period of development had little interest in and paid 
little attention to the heterogeneous aggregate of objects rejected 
from his category. Nevertheless mineralogists considered rocks 
as so plainly forming an appendix to mineralogy that they set 
up schemes for their classification based almost wholly upon 
mineral composition. 
Foundations of petrography.— While mineralogy was thus 
developing on definite lines, the students of the mineral masses 
observed to have wide distribution in the earth were building up 
a vastly more complex science. By the careful researches of 
Pallas, de Saussure, von Buch, von Humboldt, Werner, Smith, 
Macculloch, and many others, the generalizations upon which 
stratigraphic geology is based were being formulated. The 
facts of an order in the superposition of strata were established 
in several localities and the genius of Werner was devoted to 
the framing of hypotheses explaining the observations made and 
providing for the extension of generalizations to the rock 
masses of the globe. 
The foundations of petrography were laid in this period, the 
term rock (roche, Gestein) was frequently employed, and works 
