118 
BAVARIAN BASALTS 
phyritic structure, contain olivine and titanium augite as pheno- 
crysts, which are not usually recognizable except by means of 
the microscope. Phenocrysts of basaltic hornblende and biotite 
are much rarer. Plagioclase rich in lime (never of any consid¬ 
erable amount), is only to be observed in the ground-mass, and is 
very often accompanied or even replaced by a soda mineral, mostly 
nephelite, or more seldom by leucite or melilite. 
Also, macroscopically, these basalts may easily be distinguished 
from the other rocks enumerated above. The fracture is never 
crystalline but splintery. Of yet more consequence for the field 
geologist is the abundance of periodotitic fragments, these being 
usually so prominent that scarcely a single hand specimen will be 
found without them. In other instances such inclusions, though 
not abundant, are almost always visible. 
Therefore, both from a systematic and from a practical angle, 
the restriction of the name basalt to rocks as defined above is fully 
justified. 
