152 The American Geologist. Marcii, i89s 
occurs ill the Franconia sandstone and in the lowest bed of 
the Dresbach shales. It appears as minute glistening scales 
abundantly among the other mineral constituents of this for- 
mation. 
Biotitc. This mica is developed occasionally as a secon- 
dary product in the alteration of the diabase. 
Epidotc. Next to chlorite the most abundant secondary- 
mineral is epidote. It is the yellowish green variety and gives 
those portions of the rock in which it is a prominent constitu- 
ent a characteristic yellowish green color. Many amygdules 
are filled with this mineral, and in some them it is quite per- 
fectly crystallized. Quartz and epidote are contemporan- 
eously developed. Needles of epidote penetrating the clear 
grains of quartz are frequently seen. Epidote is apparently of 
later development than chlorite, although all the secondary 
products are at times simultaneously produced. 
Olivine. No olivine has yet been observed in any portion 
of this rock. Certain apparently pseudomorphous develop- 
ments of secondary products may possibly indicate the orig- 
inal presence of this mineral. There is, in the first place, a 
segregation of secondary magnetite forming the outline of a 
well-defined crystal form closely resembling the usual occur- 
rence of olivine. There is also a canal-like structure some- 
times present in the areas of chlorite which may indicate that 
it is a pseudomorph after the usual serpentinous alteration 
product from olivine. 
Chlorite. The mineral identified as chlorite is an amor- 
phous or granular or sometimes fibrous substance which has 
a uniformly deep green or bluish color. It has a hardness of 
2; it occurs in great abundance in all phases of the diabase as 
a secondary product, replacing portions of the original min- 
erals and filling cavities and interstices between them. The 
universal presence of this substance gives all varieties of the 
rock a greenish cast. It seems to be the earliest secondary 
mineral. In one of the sections a decomposing feldspar crys- 
tal is seen changed first to chlorite at a considerable distance 
from the lines of fracture, while after it in a narrow zone fol- 
lowing the original fracture are developed quartz and epidote 
in small amounts. Those localities in which the rocks are 
most free from chlorite display the most highly epidotic zones. 
