Acid Pcgmatyte in Diabase. — Jaggar. 207 
specimen or the thin section, of the secondary nature of the 
quartz. 
Large inclusions of quartz, of irregular clastic form, are 
common in the Pine hill and Granite street outcrops. These 
fragments vary in size from a few inches to a foot or more in 
diameter; they frequently have a faint rose color; in some 
cases they are coarse vein quartz, in others quartzyte. They 
have not been found by the writer in the dioryte facies of the 
rock which occurs in the vicinity of the Powder house. These 
inclusions are frequently rounded and sometimes embayed by 
magmatic corrosion; one of these is now well displayed on the 
west wall of the Granite street quarry, measuring twelve by 
three inches, with rounded contours bounded by the wreath of 
augite prisms characteristic of quartz inclusions in basalt,* and 
with a narrow-necked embayment at one end three inches in 
depth. 
The augite wreath, or more accurately, mantle, invariably 
encases these inclusions, forming in the thin section an endo- 
morphic "reaction rim" in the diabase at the contact of the 
inclusion. This mantle varies with the association in the dia- 
base; if in association with the quartz-pegmatytes the rim is 
wide, showing successive zones from the diabase to the in- 
clusion of augite, microcline, micropegmatyte and chlorite; 
if in the normal diabase the rim is a simple border of augite 
prisms. 
Thin sections (52-53) from the contact of a large quartz 
inclusion in the normal diabase at Granite street show coarse 
ophitic structure in the diabase, with biotite, augite and some 
brown hornblende. The quartz of the inclusion is clear, con- 
sisting of very large interlocking grains which show strain, 
with numerous liquid inclusions in lines; it is apparently vein 
or pegmatyte quartz. The border outline of the quartz ap- 
pears corroded and irregular, with long prisms of a green 
amphibole and chlorite penetrating it in places, and abundant 
calcite. Between this border and the diabase, closely packed 
augite prisms form a continuous zone, idiomorphicallv ter- 
minated on the diabase side, their l.ases on the inclusion side 
*Dannenberg, A.— Tschermaks Min. u. Pet. Mittli., 1894, Bd. XIV, 
P I/. . 
T.ncroix, A. Les enclaves des roches volcaniques, 1893, p. 585. 
Vide also Rosenbusch, p. 1034. Zirkel, vol. II, p. 871; vol. Ill, p. 102. 
