10(J PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
original difference in the rock from which the steatite has been altered, 
or to some difference in the conditions of alteration which allowed 
both minerals to be formed from the same origin. 
The steatite occurrences are more numerous than the serpentine, 
but except for the fact that they are found in a slightly wider band, 
their distribution as well as their form is much the same. They are, 
therefore, without doubt due to the alteration of a basic igneous rock 
in much the same way as is serpentine. In a few places the relations 
between the two rocks suggest that the parent rock of the steatite was 
an earlier intrusive than that of the serpentine. This feature is best 
seen at Waterbury where the serpentine occurs as lenses with sharp 
contacts in the steatite. The existence of sharp contacts and the 
distribution of so many lenses of serpentine throughout the steatite 
makes it seem improbable that the two kinds of rock were produced 
by different alteration from the same original intrusive. The earlier 
intrusive may have been a pyroxenite containing considerable pyrox- 
ene, and this altered to steatite. The later intrusive was more basic 
due to further differentiation and may have been a relatively pure 
dunite which later was changed to serpentine. In this connection 
it is interesting to note that an area of unaltered dunite exists further 
south in Massachusetts at Cheshire. 
