Acid PcgDiatytc in Diabase. — Jaggar. 21 1 
which is corroded and embayed. The quartz inclusion is 
made up of large interlocking individual grains of varying 
size. 
Summarizing the description of the cross-section of the 
reaction rim about the inclusion, we have an outer zone of 
augite prisms as is usual about quartz inclusions in basalt, and 
as in most cases in this diabase. But within this is a zone of 
quartz-microcline pegmatyte, of exactly the same nature as 
that which fills the cavities in the adjoining rock; and the 
microcline is developed as a zone of prisms on the inner sur- 
face of the old augite zone while the border of the quartz in- 
clusion is corroded, — phenomena that can be accounted for 
only on the hypothesis that the waters or vapors charged with 
the pegmatyte minerals forced their way through the pores 
of the old augite zone, which was not chemically afifected by 
them. The quartz inclusion they corroded, however, and sim- 
ultaneously microcline was deposited on the inner surface of 
the augite mantle, and last of all the micropegmatyte mixture. 
An inner zone of acid feldspar about a quartz inclusion 
has been described by Dannenberg* in basalts of the Sie- 
bengebirge, and his succession of zones closely resembles that 
of the ^ledford diabase. He notes next within the augite 
zone a band of large fan-shaped bundles of feldspars of higher 
acidity than the feldspar of the basalt, but he does not state 
whether these are developed radial to the inner surface of the 
augite mantle or to the quartz surface. He notes an inner or 
second augite zone with prevalent skeletal structures; this 
we have also observed occasionally. 
Mention was made in a preceding paragraph of the infil- 
tration minerals observed in the thin section of the diorite 
facies of the rock. Merrill f has called attention to the extra- 
ordinary depth to which the post-glacial disintegration of this 
rock has gone, largely due "to its coarse and somewhat granu- 
lar structure;'" it is highly miarolytic, the ophitic framework 
of feldsjjars forms a sort of "sponge" support when much 
degeneration has gone on in the interspaces. Just as such a 
*Danneberg, A., Studien an Einschliissen in den Vulkanischen Ges- 
teinen des Siebengebirges, Tschennaks Min. u. Pet. Mittheilungen, 
1894, Bd. XIV, p. 17. 
tBull. Gcol. Soc. Amer., vol. \\\. pp. ,?4g-362, 1896. 
