EXPLANATION OF PLATE 5. 
Figure 1.—From photograph of hand specimen, nearly natural size; 
represents a rock of three generations of spherulitic growths. 1st. “ Hol¬ 
low ” spherulites (p. 422), many of them crushed by movements of the vis¬ 
cous mass. 2d. “ Trichitic ” spherulites (p. 423); the small white arms often 
in bunches or groups; cross-sections of these arms shown in center of 
specimen. The dark central part contains fresh trichites, the white color 
of the outer zone being due to decomposition of the trichites. 3d. “ Sup¬ 
plemental” spherulitic zones (p. 424), comprising in this rock almost the 
entire mass between the earlier growths. This part has a dull brown 
color, subconchoidal fracture, and opalline luster. 
Figure 2.—Photomicrograph, X 25, ordinary light. In center a “ hol¬ 
low ” spherulite of botryoidal form. Branching feldspar needles radiate 
from several centers and run to circumference, but are obscured by ferritic 
flakes. The development of tridymite is shown by the lighter parts of the 
spherulite, and the consequent exclusion of ferritic matter caused the 
outer zone to be very dark. Several small balls of tridymite are seen in 
this outer zone. 
On surface of the hollow spherulite are numerous balls of tridymite, 
surrounded by dark zones filled with ferritic matter. Each of these tridy¬ 
mite balls is a center for the development of a wavy concentric structure 
and of a delicate radiate growth of feldspar needles. Compare with de¬ 
scriptions, page 423. This “ supplemental ” spherulitic development also 
surrounds the sanidine crystal on the left of the hollow spherulite. This 
rock contains no trichitic spherulites, and the crystalline parts above de¬ 
scribed are surrounded by fresh colorless glass, shown on the upper edge 
of the figure. 
(441) 
