438 JAS 22, (C(QULISML ANG 
Near the southern end of the ridge an irregular dike a few 
feet wide crosses the gneissoid rock, reminding one of pegmatite. 
It is white and consists of immense individuals of nepheline and 
muscovite, often several inches or even a foot long, with small 
patches of blue sodalite. No feldspar was seen in the dike, 
unlike examples described by Adams,’ and no corundum was 
found in it. 
As usual in nepheline-syenites there is great variation from 
point to point in the rock, easily seen on weathered surfaces and 
still more marked in thin sections. Adams finds, as essential 
ingredients of the outcrops near Bancroft, nepheline, plagioclase, 
and biotite or hornblende in small amounts; but scapolite and 
calcite usually occur, as well as various minor accessory minerals. 
Thin sections from the locality here described show more variety 
in constitution. All the minerals mentioned, except hornblende, 
occur, and the feldspars include orthoclase and also a little 
microcline as well as microperthite. The soda-lime feldspars are 
generally present in much larger amounts than the potash feld- 
spars, and seem to have a wide range in composition as deter- 
mined by optical means. A few have angles of extinction of 
4° or 5° from the twin plane and appear to be albite as in the 
rock examined by Adams, others having a very small angle are 
probably oligoclase, while a considerable number range from 
17° to 23° indicating labradorite. Some have broad and sharply 
cut twin lamellae, others very narrow and obscure ones. All 
the feldspars are beautifully clear and fresh as a rule, much more 
so than those of the associated Laurentian gneisses and granites. 
The nepheline also is generally very fresh and, as mentioned 
by Adams, has not the color nor oily luster of eleolite, though 
it seldom shows crystal forms. Large individuals often contain 
inclusions, minute crystals of hornblende, of biotite, and long 
rows of tiny dots of a transparent doubly refracting mineral. 
Calcite inclusions sometimes occur completely enclosed in fresh 
looking nepheline. In one example the somewhat weathered 
nepheline contains crowds of slender transparent fibers or 
"lbid., p. 11. 
