Classification of Massive Rocks. 305 
(B) basaltic nephelinites, usually porphyritic, with less 
nepheline and more augite than the doleritic 
varieties. 
(c) phenolitic nephelinites, porphyritic varieties with nephe- 
ine in two generations and a light-colored augite 
(acmite) only in the ground mass, 
(D) camptonitic nephelinites, porphyritic varieties with a 
base composed principally of nepheline or a glass 
with the composition of this mineral, and numerous 
porphyritic crystals of augite and hornblende, some- 
times in two generations. 
2. NEPHELINE-BASALTS, olivine-bearing. The prevailing types 
are those corresponding to the doleritic and basaltic 
nephelinites. 
J. THE MELILITE ROCKS. 
Melilite rocks are also confined to the neovolcanic class. They 
have no representatives among either of the other classes. They 
consist essentially of melilite, olivine and augite. 
Their normal structure is the holocrystalline porphyritic, in which 
olivine, augite and biotite, and sometimes melilite, occur in two 
generations, although the last-named mineral is more commonly 
found only in the groundmass. 
The separation of the group into two varieties :— 
(A) melilite-basalts, and 
(B) alnéites, rests almost entirely upon geological grounds. 
The alndites, however, are much richer in augite 
than the melilite basalts, and also contain more 
biotite. 
K. THE LIMBURGITES AND AUGITITES. 
This group includes rocks composed in larger part of pyroxene, 
with or without olivine. They usually contain also a little plagio- 
clase and hornblende. : ; 
_ Their normal structure is the hypocrystalline porphyritic, though 
Sometimes they become completely amorphous through the absence ` 
of porphyritic constituents. 
They are divided into :— 
1. Loweurarres, which are olivine-bearing, and 
2. ÅUGITITES, which are olivine-free. 
Colby University, Waterville, Me. 
