COMPOSITION AND STRUCTURE OF THE ROCKS-WERNER. 21 
formahle position. When the angle of inclination is difTercnt, 
the uppermost is said to occupy an unconformahle position. 
The iincoiifoi’inable and over/i/inff position, is where a rock lies 
over the edges of the other slratum. It is the position of lava, 
and of basalt, from whence, as well as from other circumstances, 
the latter is inferred to be of igneous origin. 
COMrOSITION AND STKUCTURE OF THE ROCKS. 
12. The word rock, is used by Geologists, in a sense some¬ 
what difl’erent from its common acceptation, for the large mineral 
masses that form the crust of the earth, whether aggregated into 
solid bodies, or not. The names and characters of the sim])!e 
minerals, which constitute the rocks, have been given. Whole 
mountains are sometimes formed, essentially of a single mineral, 
as ([uartz or limestone. In other cases, two or more enter into 
the composition of the same rock, as in granite ; and are either 
in a state of intimate mixture, or separate and distinct. 'J'he 
masses thus formed exhibit several varieties of structure, as the 
granular, slaty, laminated or tabular, cellular, which require no 
definition ; porphyritic, when cr 3 'stals or grains are imbedded 
in a homogeneous base, and amygdaloidal, where cavities in a 
rock originall}' cellular, are filled with matter of a difl'erent kind. 
WERNER. 
13. The southern part of the kingdom of Saxony where it 
borders on Bohemia, is rich in metallic ores ; especially in the 
ores of silver, copper, lead, tin, arsenic, cobalt and iron. A school 
of INIincs is maintained by the Saxon king at Freyburg, within 
the limits of the metalliferous district, for the education of such 
persons as arc to be employed in the extraction of the ores from 
the earth, or in smelting them when brought to the surface of the 
ground. 
In this institution, Arraham Gottlob Werner, then twenty- 
five years of age, received the appointment of Professor of INIincr- 
alog}', in 1775.* He became the benefactor of this science, by giv¬ 
ing precision and accurrac)" to its language, as well as by his skill 
in tlie discrimination of mineral species, and if his system of 
description and classification are not perfect, we must not, in 
estimating his merits, forget what IMineralogy was when it pass¬ 
ed into his hands. But Werner is most cxtensivelv known and 
celebrated as a Geologist. He created an interest in his own 
favorite pursuits and studies, by pointing out the application of 
a knowledge of the earth’s structure, to the practical jiurposcs of 
mining; yet it is not easv to account for the influence excited by 
him for so long a period over the opinions of men. Ilis oppor¬ 
tunities for observation were excellent, and discovering that the 
* lie died at Dresden in 1817. 
3 
