378 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
cipal sulphides are pyrite, arsenopyrite, chalcopyrite, and galena. 
The galena occurs only in veins, so far as my observations go. 
The others are present in both veins and sediments, and much of 
the gold is locked up in them. Pyrite occurs in small cubes and 
minute granules, rarely in masses of several crystals; arsenopyrite 
is found in typical striated prisms, often half an inch long, and in 
massive form ; chalcopyrite exists chiefly in irregular masses. 
Py rite is the most abundant sulphide, and in the sediments its 
attitude is characteristic. The strata have planes of division, 
unevenly distributed, which mark the more abrupt changes in 
texture and color, and along which the flssility is more marked. 
These may be called major planes of division. Between them are 
other minor planes at which the cohesion is greater, and which 
represent smaller changes in the conditions of sedimentation. In 
the slates the pyrite lies along major planes of division, and in 
some cases along minor ones, and is scattered sparingly through 
the mass of the stratum. Rarely it is irregularly distributed in large 
quantities within the bed. This position is so constant that, where 
stratification in the slate cannot be deciphered by color-bands and 
is obscured by cleavage, layers of pyrite, if present, serve to give 
strike and dip. Usually the mineral is abundant along the base of 
a layer and decreases upward. In other instances it is plentiful in 
the center of a bed and concentrated again at the division-plane. 
In the coarser strata it is less regular in distribution, but in general 
follows the same rules as in the slates. In veins a considerable 
amount is to be found, but it has no regularity of position. Fre¬ 
quently it protrudes from the sediments into the quartz. On the 
borders pyrite is often collected in sheets, chiefly on the hanging- 
wall. It is less abundant or absent on the foot-wall. In the oxi¬ 
dized zone near the surface, all this is brought out clearly; below 
that it is not so easy to find. 
Arsenopyrite occurs most abundantly in the whin, distributed 
irregularly, often with its crystals lying at an angle to the bedding- 
planes. It is also situated sparingly along these planes, and in a few 
cases has been seen to lie directly across them, part being in one 
stratum, and part in the other. In veins it is common in massive 
form, but crystals are comparatively rare. 
The whole metamorpliic series is cleaved strongly. The strike 
of the laminae averages not far from that of the rocks in many 
localities, and is persistent throughout the series, showing unity in 
