70 ELEMENTARY GEOLOGY 
the flow structure (Fig. 25). This rather indistinct 
banding is relatively rare and quite different from that 
of other rocks. As a general statement, it may be 
said, that excepting for this, igneous rocks are massive. 
Not only do they differ from the sedimentary and meta- 
morphic strata in this respect, but they also differ from 
the former in the fact that they are usually glassy, or 
else show signs of crys- 
talline structure. 
Distribution of Igneous 
Rocks. — The eruptive 
rocks are found most 
abundantly in the neigh- 
borhood of volcanic 
cones, which are either 
erupting lava or ash at 
Flow structure in lava, enlarged by micro- 
scope. Bands bent around the porphy- Present, or have recently 
sis Sn: done so; but they occur 
in other places as well. In New Jersey, Connecticut, 
and the Palisades of the Hudson, for instance, although 
there has been no eruptive action there for many 
geological ages, lavas are found, testifying to former 
voleanic energy in volcanoes long since extinct. In 
New England, too, there are great areas of granite, and 
other igneous rocks, which were once intruded deep in 
the earth, and are now revealed by the wasting away 
of the solid blanket of overlying strata. 
