268 TJie American Geologist. November, looo 
well known play of colors, though not as beautifully as that 
from Labrador. Black particles supposed to be magnetite are 
also abundant, while liquid inclusions are rare. These have 
not been seen along curving jolanes. 
A section from the plagioclasyte of Lake Champlain, N. 
Y., shows an immense number of dust-like particles, probably 
magnetite, as w-ell as liquid inclusions, both occur along lines 
and planes, and scattered everywdiere through the mineral. 
They resemble in all essential characters those described from 
Carlton peak. No acicular inclusions sre seen here, nor do 
the ilmenite tablets occur. The abimdance of the magnetite 
particles gives the labradorite of this rock a deep black color 
but no iridescence is visible. Finally, sections from the Min- 
nesota gabbros and diabases often show the bbck acicular 
needles, but they are never accompanied by iridescence. 
As to the origin of these inclusions, it seems to the writer 
impossible to attribute them to the process of schillerization. 
or to any alteration process, since they occur in a feldspar 
often showing no evidence wdiatever of alteration of any kind, 
but perfectly fresh and glassy. They not un frequently show 
crystal form peculiar to themselves and at variance with the 
forms of the enclosing mineral. Although liquid inclusions 
frequently exist in the mineral they are rarely bounded by 
negative crystal planes and have never been seen to contain 
the colored titanic tablets, as they should if they had de- 
veloped through schillerization. But perhaps the most con- 
clusive evidence that they are original and not secondary in- 
clusions is afiforded by the fact that there is often no mineral 
in sufficient quantity from which they could have been de- 
rived. Prof. Judd would have us believe that they were de- 
rived from the pyroxenic element of the rock, but that mineral 
is not uncommonly manifestly in far too small amount to fur- 
nish the myriads of inclusions which Vogelsang has estimated 
to amount to from one to three per cent of the volume of the 
rock, and to number sometimes as many as one hundred- mil- 
lion per cubic centimeter! 
Furthermore in many large areas of plagioclasyte the 
small amount of augite which does occur is perfectly fresh, 
showing no evidences of alteration of any kind, while the lab- 
radorite mav be crowded with these inclusions. In other oc- 
