E. S. Dana—Garnets from the Trap Rocks of New Haven. 217 
to prove its absence. The magnetite was also tested qualita- 
tively for titanic acid, but none was discovered. 
The associated minerals deserve also a few words of descrip- 
tion. The magnetite stands first in order of abundance. tt 
appears in the form of brilliant octahedrons, scattered some- 
times thickly, sometimes sparsely, over the surface of the rock ; 
it uniformly underlies the garnet where they occur together. 
The octahedrons of magnetite are sometimes unmodified, but 
generally the solid angles are replaced with the planes of the 
form 8-8, and the edges beveled with those of the form 2-2; an 
m-n form is also common, but with planes so rounded as not 
to admit of determination. The development of the last form 
occasionally produces irregular bullet-shaped crystals. The 
octahedral faces are brilliant, the others dull. 
The pyroxene occurs in minute dark-green crystals, destitute 
of luster; they are crowded together on the surface of the 
rock. These crystals are strictly pseudomorphs after pyroxene, 
for though having unquestionably its form, they are so soft as 
to be easily cut with a knife, and in the powder have all the 
mp of chlorite. 
he apatite occurs in very minute prismatic crystals of a 
yellowish-green color. They are most common on and among 
the crystals of pyroxene. They are more numerous, however, 
than would appear at first glance, since a careful examination 
shows that they interpenetrate the garnet crystals in great 
numbers. The crusts of garnet particularly, which are appar- 
ently perfectly homogeneous, are found when broken up to be 
penetrated in every direction with these minute apatite needles. 
In this respect the garnets resemble those of the Kaiserstuhl 
described by Knop: 
- 
inally, the caleite is found in crusts, and in rhombohedral 
the above minerals are here true secondary apes 
ably in 
cite; the excess of silica above that needed by the garnet, and 
also the alkalies have disappeared entirely. 
Am. Jour. ——s Vou. XIV, No. 81.—Sxpr., 1877, 
