304 Classification of Massive Rocks. 
(B) leucite-tephrite, in which leucite replaces the nepheline 
of the tephrite. 
(c) leucite-nepheline-tephrite, containing both nepheline and 
ucite. 
2. BASANITES contain olivine as an essential constituent. The oli- 
vine is ‘almost always present in porphyritic crystals. 
The basanites are subdivided, like the tephrites, 
into :— 
(A) nepheline-basanites. 
(B) leucite-basanites. 
(c) leucite-nepheline-basanites. 
H. THE LEUCITE ROCKS. 
The leucite rocks are unique, in that they occur only in the 
younger effusive series. They contain leucite instead of feldspar 
as their principal component. With this is always associated 
augite, and frequently biotite. The occurrence or non-occurrence 
of olivine serves as a means of separating them into two 
divisions :— 
1, LEUCITITE contains no olivine. Its structure is panidiomor- 
phic- to hypidiomorphic-granular, although it occa- 
sionally becomes porphyritic through the develop- 
ment of leucite and augite in two generations. 
2. LEUCcITE-BASALT contains olivine. Both olivine and augite 
usually occur in porphyritic crystals, leucite rarely 
or never. Their structure is porphyritic. 
I. THE NEPHELINE ROCKS, 
Like the group of the leucite rocks, the present group, which 
embraces rocks composed principally of nepheline and augite, 
no equivalent among the intrusives or the palzovolcanic class. 
The prevailing structure is the porphyritic with the iron-bearing 
silicates and olivine, when it is present, and sometimes nepheline as 
the porphyritic constituents, while the ground mass is hypoerystal- 
line, and made up in large part of nepheline. 
The nepheline rocks are separated into two divisions :— 
1. NEPHELINITES, which contain no olivine. These are subdi- 
vided, according to structure, into :— 
(a) doleritic nephelinites, which are coarse hypidiomorphic 
granular varieties. 
