MEMBERS OF THE PYROCRYSTALLINE CLASS. 
63 
§ 50. The laminated pyrocrystalline rocks. They possess 
the first characteristic of the preceding class. Their second 
characteristic consists in the arrangement of the component 
minerals into parallel bands or stripes. In the third character¬ 
istic they agree again with the preceding section. They are 
referred to under the second phase of the preceding section. 
§ 51. The pyroplastic rocks. The first characteristic consists 
in their homogenity, or an approach to it. When compact, 
they are perfectly homogeneous; when granular, it is sometimes 
possible to discover the mixed nature of the mass by the occur¬ 
rence of whitish particles in a granular ground, or the ground 
or base may furnish individuals distinguishable in size, as the 
basalts, the greenstones, trap, and porphyry. They belong to 
rocks indicated under the third phase of the section already 
referred to. The mass may be laminated, or rather sheeted, 
columnar or massive, or the mass may be vesicular, but the 
vesicles are not empty. The circumstances connected with 
their cooling have modified their structure. A part have cooled 
beneath water, or the sea, and a part have cooled in the atmo¬ 
sphere, and hence the subdivision of the class into submarine 
and submrial. The subserial products are numerous. They may 
be porous, vesicular, glassy or vitreous and compact; vitreous 
and fibrous, like hair, or in the condition of an ash. In the 
vesicular structures, the vesicles are usually empty. They are 
referred to under the fifth and sixth phase of § 48. They are 
the modern volcanic products. 
OF THE MEMBERS OF THE MASSIVE PYROCRYSTALLINE 
CLASS. 
§52. Granite. The primary,hypogene and igneous, of differ¬ 
ent authors. It consists of feldspar, quartz and mica, commingled 
together, forming a mass in which their arrangement has no 
order which can be discerned. Each mineral may predominate 
in different localities, though it is rare for the quartz to exist 
in excess over and above the feldspar and mica. The individual 
minerals have no allotted size; the mass may consist of small 
