220 The Americati Geologist. October, 1900 
are completely surrounded by rims of magnetite which are 
certainly of later date, probably in part secondary. A large 
mass of magnetite with clearly defined crystal outlines serves 
to explain the occurrence. At a certain stage of its growth 
the crystallization of the augite crystal was seriously inter- 
ferred with by a crystallization of iron oxide over its surface. 
This prevented the central mass from perfecting its form and 
showing good crystal faces, but did not prevent it from con- 
trolling the orientation of other pyroxene elements as they 
crystallized. It is interesting in this connection to note that 
the magnetite rims are noticeably thicker on the side of the 
augite farther from the large magnetite crystal, as if the iron 
were intercepted on its way to that crystal; indeed on the small 
crystals of augite next to the magnetite the rims are very nar- 
row or entirely lacking. This augite area is also interesting 
since it shows quite clearly the decomposition of the pyroxene, 
first by the appearance of the diallagic parting and then by 
transformation to clinochlore, usually with accompanying sec- 
ondary magnetite. At the same time it shows bands of sec- 
ondary hematite which follow.no law of direction, but propa- 
gate themselves irregularly through the pyroxene in a manner 
very similar to the serpentinization of olivine. 
Primary Minerals. 
The primary minerals of the plagioclasyte are: labradorite, 
augite, magnetite and apatite. These will be passed in review, 
giving all the characters of each which it has been possible to 
determine with the material at hand. 
The LABRADORITE Is by far the most important mineral of the 
rock, making up as it does frequently more than ninety per 
cent of the whole. As is well known it takes its name from 
the peninsula of Labrador on whose coast it was first found by 
Wolllf about the year 1770. It would be useless to enumerate 
the various names which it has recerved, such as labradorstein, 
kalkoligoklas, mornite, silicite, radauite, chatoyant or opaline 
feldspar, etc.; but it may serve a purpose to show clearly the 
varying use of the name according to the authorities who have 
made a special study of the feldspars during the last few years. 
It is to Tschermak that we owe the theory of an isomor- 
phous series comprising all the plagioclase feldspars from al- 
