2o8 The American Geologist. April, nsss. 
a mass of chlorite and calcite. Chlorite is the chief secondary 
product from the augite, fiUing all the cleavage cracks. The 
hornblende and feldspar of the diabase are allotriomorphic to the 
augite rim, while the ores and apatite are of earlier generation. 
Two other quartz inclusions (50-51) from the northern 
wall of the Granite street quarry, where the rock is filled with 
a net-work of the salmon-colored quartz-microcline veinlets 
and the diabase is full of interstitial quartz, show a remarkable 
modification of their pyroxenic mantle. In the hand-speci- 
men the quartz has a faint rose tinge in one case, in the other 
it is turbid with inclusions. The zone of alteration in the 
diabase is from seven to fourteen millimetres wide. In the 
case of the smaller specimen, the inclusion has broken out of 
its trap matrix bounded by the outer layer of this alteration 
zone which forms over it a smooth rounded scaly coating 
of greenish black color. 
A thin section of this reaction rim shows, to the naked 
eye, an outer layer of augite prisms arranged mostly with their 
prismatic axes (c) normal to the original inclusion surface, and 
with idiomorphic terminations on the diabase side. Their 
basal terminations form in section a continuous flowing line, 
which, as will be seen later, represents the original surface of 
attachment. ■ On- the opposite side of this line, that is, de- 
veloped towards the quartz inclusion, on the inner side of the 
outer augite band, is a line of squarish pink feldspar prisms. 
On the inner surface of this zone is a thin green line of chlor- 
ite substance locally defined, and within that sometimes a sec- 
ond feldspar band is seen, but not continuous. 
With the aid of the microscope, this thin section may be 
resolved into six zones, represented in figure i by D, DF, A. 
F, M, and Q, passing from the matrix rock (D) to the quartz 
inclusion (0). The description of these zones, in order, is as 
follows: 
DIABASE. (D). The outer portion of the section, two 
millimetres from the augite band, is a coarse-grained diabase, 
with huge feldspars of the acid labradorite group enclosing- 
triangular spaces filled with the ferro-magnesian constituents. 
The feldspars are twinned on the Carlsbad and albite laws, and 
thus ofifer excellent subjects for determination by Michel 
Levy's method. The composition Abj An ^ was determined 
