102 The American Geologist. February. 1905 
pale bluish shades like talc. Often also the serpentine is 
gathered in bright emerald or bluish green patches. The 
diallage is often quite fresh and shows clearly two pinacoidal 
cleavages, with rarely any trace of the prismatic cleavage. 
It is pale yellow with few of the enclosures characteristic of 
the mineral, shows the usual fibrous structure and often dis- 
tinct twin lanimae interposed in the plane of the perfect 
cleavage. It is in many cases advanced beyond the olivine 
in the change to serpentine and the brightly colored varieties 
of the latter mineral are most closely connected with it. 
Other smaller and often perfectly outlined crystals pos- 
sess the cleavage and show the ordinary twinning of augite 
and are often enclosed in the plagioclase. 
The feldspar, wedged in sharply angular pieces among 
the other constituents, shows twin-lanimae of very unequal 
widths, with extinction 21 to 27 degrees. In one section 
parallel to M. the extinction was 29 degrees. Octahedra 
apparently of picotite occur in the olivine and serpentine, 
while magnetite appears both as an original constituent and 
in smaller granules in the serpentine. 
The order of crystallization is picotite and magnetite, 
olivine, diallage, augite, plagioclase. The rock affords slides 
of great beauty from the very regular forms of its crystals 
and the beautifully developed sepentinous change. 
In this connection I wish to call attention to certain 
allied eruptive rocks from Frobisher bay, among the collec- 
tion made by C. F. Hall, which I studied twenty-five years 
ago with improvised optical apparatus. 
Hornblende-bearing Diabase. — This is a dark fresh 
looking trap the feldspar needles just showing to the eye. 
The feldspar rods are labradorite with irregular twinning in 
few bands. A broad central area is dusted brown, and this 
dust decreases toward the edge, and a strong undulose ex- 
tinction goes parallel with it, the angle of extinction decreas- 
ing toward the border. Large grains of a pale coarse-cleav- 
ing pyroxene occupy the meshes, mostly uralitized. A con- 
siderable number of large grains of an original greenish- 
brown hornblende appear. This was described in Hall's 
Narrative, p. 568, as quartz dioryte. 
Alnoyte. — So many large blocks of this rock were in 
