TERTIARY VOLCANIC ROCKS-BRECCIA. 
99 
in a true breccia, composed, however, almost exclusively of fragments of latite- 
phonolite. 
Granite (or schist or gneiss) brecciated in place in a similar manner occurs 
in narrow zones at several places along the contact, and in larger areas on the 
southern slopes of Carbonate and Mineral hills. The material is almost exclu¬ 
sively granite, with a rare fragment of volcanic rock. The grains are angular and 
appear to have suffered little dislocation. Only careful examination distinguishes 
this rock from massive granite, into which it grades. Its presence in considerable 
amounts at the northern edge of the main area seems to indicate that violent 
forces were at work at that place, but that they were not sufficient to wholly 
remove the shattered material, as was done in other places. This brecciated granite 
is not to be confounded with breccia, like that near the summit of Mineral Hill, 
composed largely of granite fragments which are not so strictly of local derivation. 
Granitic breccia of this kind is more or less loose and shows a sharp contact with 
the massive granite. 
Fragments of vesicular, glassy rock have been found in some of the outlying 
breccia areas—for instance, in the small mass near the southwest corner of the 
area mapped and in one specimen from Copper Mountain. No material of this 
kind has been found in the main breccia mass, though the great decomposition 
which this fragmental rock has in many places undergone makes it impossible to 
speak with certainty on this matter. 
On the dump of Stratton’s Independence No. 2 shaft occur a few blocks of 
interesting material. It is a fine-grained, structureless tuff of light color, some¬ 
what dolomitized, holding numerous small round pellets, nearly white, and var} T ing 
from 1 to 6 or 8 mm. in diameter. Many of these have, instead of a single curved 
surface, a botryoidal or mammillary form, suggestive of concretions. When these 
are broken it is seen that a thin shell incloses material similar to that of the main 
portion of the rock. A thin section containing one of these pellets shows that 
the shell is made up of the same materials as occur both outside and inside of it, 
only of much finer grain. The interior of the globule seems to hold more carbonate 
than the material outside. 
Whether these globules represent accumulations about drops of water,® and 
hence indicate the presence of surface conditions, or whether they have been 
formed by concretionary depositions from perhaps carbonated waters, and hence 
may have originated at a distance from the surface, it seems impossible to decide. 
The microscope confirms the conclusions reached from an examination in the 
field. With the exception of the fragment of leucitophyre already described and 
the few occurrences of vesicular rock mentioned above, not a single mineral or 
particle of original material was seen in the scores of thin sections of breccia exam¬ 
ined which is not represented in known areas of massive rock occurring in the 
district. The most prominent constituent is phonolite, usually in fragments which 
show only the trachytic groundmass, but occasionally phenocrysts are seen. But 
little less abundant are similar fragments of latite-phonolite. Next in abundance 
are broken phenocrysts of fyddspar from these tWo rocks. Grains of magnetite 
from the latter are also common in some specimens. Broken grains of quartz, 
“Cl. Howe, Ernest, Recent tuffs of the Soufri&re, St. Vincent: Am. Jour. Sei., vol. 16, 1903, pp. 319-320. 
