38 ARCTIC BASALT PLATEAU 
indicate some enstatite-augitic affinity,! thus FeO and MgO domi- 
nating over CaO. A feeble zonal structure with decreasing axial 
angle and birefraction to the centre, and a faint pleochroism in 
yellowish and greenish tints strengthen this affinity, as dropformed 
glassy inclusions too, arranged in files parallel to (001). The second- 
generation-augites are only occasionally developed as minute grains, 
between crossed nicols on the black ground appearing as lighting 
points, who increase in importance and dimensions with decreasing 
glass content. In the greater part of the specimens the second 
generation of augite is oppressed. — The olivine is apparently 
crystallized only in the grained rocks, in which the glass is less 
abundant, and even here it is subordinate, appearing as small 
rounded grains, mostly pseudomorphosed to a brownish-red, pleo- 
chroic and fibrous aggregate of ironbearing serpentine (?), optically 
negative and with relatively high birefraction, and to a reddish-brown 
isotropic mass, perhaps due to resorption. The grains are rounded 
and of small size and apparently crystallized after the first appea- 
rance of augite; in the glassy rock it is quite wanting. — Apatite 
in small and scarce needles was detected only in rocks poor in glass, 
where the ore mineral is well individualized as sharp octahedrons 
of magnetite. In the glassy rock the magnetite forms dendritic ske- 
leton crystals of minute size contributing to the dark colour of the 
glass. 
Besides the inclusions of sedimentary rocks mentioned above (p. 
17) the basalt contains great allogenic fragments of a polysynthe- 
tical twinned albite-oligoclase (12 °/o An), and of a greenish diopside 
of somewhat divergent optical properties (2 Vy—=56#°). 
The sphaerules are yellow to dark brown transparent in sections. 
The smaller ones are isotropic, but in the greater ones they develop 
radiating structure with birefracting radii, optically negative; this 
birefraction seems to be in close connection with the progress of 
‘9g p. 1—131. 
