GEOGNOSY AND GEOLOGY, 205 
In Germany it occurs in the Hartz, in Westphalia, in the trans-Rhenish 
Palatinate, in the Odenwald, the Schwarzwald, in Saxony, Silesia, &c. 
D. Amphibolic Rocks. 
Of these, diorite is the most conspicuous. It forms veins rather than 
independent masses. Where it occurs of greater extent, it exhibits rough 
mountain forms, a character conspicuously impressed upon the individual 
rocks. This, as in syenite, is caused by the decomposition of the feldspathic 
substance, most generally albite, thus leaving the harder hornblende in the 
form of projecting asperities. 
EK. Pyrozxene Rocks. 
These form both single smaller block masses, and entire connected series 
of mountains, as also veins and injected pseudo-morphous strata between 
normal strata; they also constitute caps extending over other rocks. The 
cleavage takes place in various ways; in curved surfaces, in acute angled 
parallelopipedons and in columns, which latter often exhibit a striking 
similarity to those of basalt, and are especially peculiar to trap. The 
curved surfaces frequently exhibited by diabase are often globular, with 
concentric scaly lamination. Diabase of this character is not unfrequently 
called ball rock. 
A particular modification of diabase, the shell-stone, has often a stratiform 
appearance, or pseudo-stratification. The external features of the pyroxenes 
have many peculiarities. Where they form large masses, the mountains 
present steep declivities, studded with rugged rocks; where they are 
surrounded by normal masses, the single portions project in a dome form 
from them. Diabase amygdaloid is intimately connected with compact 
diabase, and gradually passes into it; the amygdaloid occurs especially in 
the external portions of the rock, the compact occupying the nucleus. 
Veins of no inconsiderable importance traverse the pyroxenes, containing 
hematite, specular iron, quartz, chalcedony, &c. The trap, trap porphyry. 
and trap amygdaloid, exhibit veins in which manganese minerals occur with 
barytes, calcareous spar, and arragonite. Copper and selenium ores are 
found in veins between diabase and the transition slate, at Lerbach, 
Tilkerode, and Zorge, in the Hartz. 
The pyroxene rocks are not readily weathered, but form, in time, 2 
tolerably good ferruginous soil. The rocks most frequently penetvate the 
strata of the transition slate, and of the bottom series. The most trap, trap 
porphyry, and trap amygdaloids, as also some euphotides, are newer than 
the carboniferous formation, in overlying the limestones of the latter. Some 
plutonic pyroxenes appear to be newer than the variegated sandstone. Of 
other masses, it penetrates syenite, granite, eurite-porphyry and allied rocks, 
and is often traversed by granite. 
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