COMPOSITION AND STRUCTURE OP THE ROCKS WERNER. 21 
formable position. When the angle of inclination is different, 
the uppermost is said to occupy an unconformable position. 
The unconformable and overlying position, is where a rock lies 
over the edges of the other stratum. 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. 
COMPOSITION AND STRUCTURE OF THE ROCKS. 
12. The word rock, is used by Geologists, in a sense some- 
what different 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 simple 
minerals, which constitute the rocks, have been given. Whole 
mountains are sometimes formed, essentially of a single mineral, 
as quartz 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. The 
masses thus formed exhibit several varieties of structure, as the 
granular, slaty, laminated or tabular, cellular, which require no 
definition ; porphyritic, when crystals or grains are imbedded 
in a homogeneous base, and amygdaloidal, where cavities in a 
rock originally cellular, are filled with matter of a different 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 Mines is maintained by the Saxon king at Freyburg, within 
the limits of the metalliferous district, for the education of such 
persons as are 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, Abraham Gottlob Werner, then twenty- 
five years of age, received the appointment of Professor of Miner- 
alogy, in 1775.* He became the benefactor of this science, by giv- 
ing precision and accurracy to its language, as well as by his skill 
in the discrimination of mineral species, and if his system of 
description and classification are not perfect, we must not, in 
estimating his merits, forget what Mineralogy was when it pass- 
ed into his hands. But Werner is most extensively 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 tbe practical purposes of 
mining ; yet it is not easy to account for the influence excited by 
him for so long a period over the opinions of men. His oppor- 
tunities for observation were excellent, and discovering that the 
* He died at Dresden in 1817. 
