100 ; GEOGNOSY AND GEOLOGY. 
alternating with the tabular spar. Oxyde of iron sometimes penetrates the 
rock in considerable quantity, forming a poor ironstone. The presence of 
much tale gives it a soapy feel. 
Section 7. Hypersthene. 
Under this head, which includes rocks in which hypersthene is mixed 
with feldspar, or some allied mineral, are especially distinguished : 
Hypersthene rock. This is a crystalline granular aggregation of labra- 
dorite or saussurite with hypersthene. The latter exerts the greatest 
influence on the rock, often occurring in so great quantity that the 
feldspathic mineral is entirely removed. Hypersthene rock is therefore of 
a dark color, and resists in a remarkable degree the action of the weather. 
The addition of chlorite converts it into diabase, and when diallage enters 
into combination it becomes euphotide. 
Section 8. The Huphotides. 
In these rocks diallage is combined with labradorite or saussurite. ; 
Euphotide (gabbro, granitone). This is a crystalline granular combi- 
nation of the above-mentioned minerals. Diallage is generally the prevailing 
constituent of this exceedingly hard rock. The color is that of diallage, an 
undefined grey passing into brown. Hypersthene and some other minerals 
are often added. It passes into hypersthene rock, more rarely into the rocks 
of the following order ; it resists, almost entirely, the decomposing action of 
the atmosphere. 
Order 5. Rocks of Schiller Spar. 
Schiller spar or metalloidal diallage, which is a well known mineral, is 
also entitled to a place among rocks. It is either pure, or mixed with 
saussurite. Should the latter be the case, it 1s often variolitic, the saussurite 
being separated in round particles surrounded by schiller spar. In 
porphyritic schiller rock, distinct crystalline foliated masses of schiller spar 
occur. Common schiller rock (primitive greenstone) often alternates with 
serpentine, and in fact bears a considerable resemblance to it. It is either 
pure compact schiller spar, or else mixed with a little saussurite. 
Order 6. Serpentine Rocks. 
The rocks of this order contain serpentine as their characteristic 
constituent. 
Serpentine Rock. Serpentine, like schiller spar, ranks both as a minerai 
species and as arock. It is principally common serpentine that occurs in 
the latter condition, the precious and fibrous being restricted to small 
portions of its mass. Green is its peculiar color; the different shades, other 
than this, depend on the presence of foreign substances. It is exceedingly 
rich in foreign species, among which asbestos, pyrope, magnetic oxyde of 
iron, &e., are the most conspicuous. 
Ophite. This rock, so much used, especially for purposes of art, is a 
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