KINDS OF ROCKS. ~ 451 
kind which afforded, on analysis, Silica 52°14, alumina 29°17, iron 
oxide 3°23, magnesia 0°76, lime 10°81, soda 3°02, potash 0°98, ignition 
0:58=100°92. 
3. Hypersthenyte.—A rock resembling the preceding, con- 
sisting of cleavable labradorite with ¢rwe foliated hyper- 
sthene; from St. Paul’s, Labrador, and some other localities. 
4. Doleryte. (Basalt, Trap.)—Chief constituents, labra- 
dorite and augite, with magnetite, and sometimes anorthite. 
Often porphyritic, and the feldspar crystals may be anor- 
thite. Amount of silica yielded on analysis usually 47 
to 52 per cent. Texture crystalline-granular to aphanitic; 
and often, especially in the latter, having glassy particles 
among the crystalline, or even an unindividualized base 
or magma between the crystalline grains—the variety called 
Basalt ; often coarse granular through the body of a dike, 
while aphanitic along its walls, and sometimes containing 
glassy portions in the latter when not elsewhere. Colors 
dark grayish to bluish-black, greenish-black, and brownish- 
black. G.=2°75-3:1. Eruptive; also metamorphic. 
It includes the larger part of the rock usually called trap, abundant 
in most regions of igneous eruptions ; constitutes the ‘‘ tray” ridges 
of the Connecticut Valley, the Palisades of New Jersey, ard similar 
ridges in Nova Scotia and North Carolina; also in the Lake Superior 
region, and extensive beds of so-called basaltic rocks over the Rocky 
Mountain slopes west of the Front Range, The rock of New Haven, 
Conn., from West Rock, afforded Silica 51°78, alumina 14°20, iron ses- 
quioxide 3:59, iron protoxide 8°25, manganese protoxide 0:44, magne- 
sia 7°63, lime 10°70, soda 2:14, potash 0°39, loss by ignition 0°63, phos- 
phorus pentoxide 0'14=99 89; G.=3:03. A hydrous or chloritic variety 
from Saltonstall’s Ridge, near New Haven, afforded Silica 49-28, 
alumina 15°92, iron sesquioxide 1:91, iron protoxide 10°20, manganese 
protoxide 0°37, magnesia 5:99, lime 7°44, soda 3°40, potash 0°72, water 
3°90, carbon dioxide 1:14=100°72 ; G.=2°86. 
_ VaRIETIES.—There are two series: A. Ordinary, B. Chrysolitic, 
and for the latter the name Peridotyte has been usec. Each occurs: 
a. aihydrous ; b. hydrous, or chloritic, of feeble lustre ; c. amygda- 
loidal, as well as chloritic; d. vesicular, or scoriaceous, as in doleritic 
or basalticTavas. Spilite is amygdaloid. 
Again, each of these varieties may be porphyritic. Again, the augite 
may be in distinct crystals. 
A coarse-granular kind, having the pyroxene foliated, is sometimes 
called gadbro. 
This basic rock, doleryte, is often called, also, basalt, especially 
when it has an unindividualized base ; a specimen of this kind, from 
Nevada, is represented in fig. 7, page 418. The name, anamesite, 
has been used for an aphanitic kind, but is unnecessary. The term 
diwbase is sometimes applied to dolerytes older than Tertiary It was 
formerly supposed that the former differed from the latter in being 
