GEOGNOSY AND GEOLOGY. 99 
different. It is therefore a matter of some doubt to which the name shall 
be applied in restricting the appellation. The name is derived from a 
species of rock which forms a cap on the Scandinavian Trapp-berg, 
elevated in a terraced or step-like manner. This rock is now assumed as 
the typical trap. It is a mixture of augite and some feldspathic mineral, 
generally labradorite, or its compact variety, saussurite. 
Trap Proper. This rock varies in respect to the distinctness of its 
ingredients, and is of a very dark color, owing to the augite. When oxyde 
of iron pervades the mass it imparts a brownish shade. It occurs 
porphyritic, granular, and compact. Trap porphyry, which contains 
erystalline labradorite or feldspar in the trap mass, is sometimes called 
melaphyre. : 
Amygdaloidal Trap is a compact trap, with cavities containing various 
minerals. The principal of these are either silicious, as amethyst, 
chalcedony, opal, &c., or zeouitic, as mesotype, stilbite, desmine, apophyllite, 
harmatome, &c.; likewise, calcareous spar, spathic iron, and brown iron 
ore. The occurrence of manganese ore is of especial economical import- 
ance. 
Section 6. Diabase. 
The mineral predominating in these rocks is hypersthene, which occurs 
in combination with some feldspathic material, as labradorite, albite, and 
with chlorite. The amount of labradorite is not inconsiderable, yet it has 
not as much influence on the color as the chlorite. This color is green 
with the latter mineral. Diabase mixtures exhibit a tendency to intimate 
combination, on which account tle crystalline structure disappears more 
or less, and this in proportion to the extent to which the earthy chlorite is 
distributed in the rock. 
Diabase Proper (greenstone), which is of a granular porphyritic and 
compact character, is very hard and difficult to break; the color is dark in 
proportion as it contains hypersthene, or augite, and chlorite. 
Greenstone Porphyry is an intimate diabase combination from which 
sparry or compact feldspar, labradorite, saussurite, or oligoclase, is separated. 
Variolite. A diabase of a dark color, with roundish light particles: 
included. 
Amygdaloidal Diabase. This is a fine grained diabase in which lie 
amygdaloidal, or undefined masses of brown spar, or calc spar. Variolite 
(Blatterstein) is, on the whole, a compact rock of an earthy fracture. Its 
colors vary between green, grey, brown, and black; the first of these. 
predominates. Genetically. considered the rock seems to have acquired 
the amygdaloidal character by the influence of vapor, ascending gaseous 
bubbles leaving cavities which were subsequently filled by infiltration. The 
slaty diabase amygdaloid or tabular spar, distinguished from the preceding 
by its laminated texture, presents other marks contributing essentially to its 
specific character. In its green or brown mass there lie spheroids which 
are frequently flattened. In this case the flattened sides lie parallel to the 
planes of stratification. Chlorite may occur separated like cale or brown 
spar. The calc spar passes into compact limestone, which then forms beds 
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