CONSTANTS OF ROCKS. 
57 
In the table giving a summary of results (see page 69), the values given 
for this rock represent the mean of these highly divergent readings and 
should be used only in the light of the explanation given above. 
9000 
7000 
5000 
ZOOO 
JOOO 
240 
FIG. 22. Green Gabbro, New Glasgow. Stress-strain curves. 
OUVINE DIABASE, NEAR SUDBURY, PROVINCE OF ONTARIO, CANADA. 
This is a very typical fresh olivine diabase, which occurs in the form of a 
large dyke, cutting rocks of Huronian age just northwest of the Murray Mine 
near Sudbury. It is one of a number of similar diabase dykes, which 
occur in this district of great nickel-bearing gabbro intrusions. It is rather 
coarse in grain for a diabase, but nevertheless much finer in grain than any of 
the granites described in this paper, except that from Westerly, Rhode 
Island, these two rocks being approximately equal in coarseness of grain, 
although differing entirely in structure. The rock is composed of violet- 
brown augite, pale green olivine, colorless plagioclase, and opaque black iron 
ore. There is also a very small amount of accessory biotite, a few minute 
acicular crystals of apatite, and an occasional minute grain of pyrite. The 
augite presents the usual microscopical characters of this species, and is 
very fresh, scarcely a trace of decomposition being anywhere discernible 
in it. The olivine, which crystallized before the augite, and therefore often 
occurs as inclusions in it, while for the most part fresh, is in many places 
partially altered to a deep green serpentine. It is much less abundant 
than the augite. The plagioclase occurs in the usual sharp, well-defined, 
lath-like form, always showing polysynthetic twinning according to the 
albite law, which in the same individual is often combined with twinning 
according to the pericline or Carlsbad law. It is fresh and brilliantly polar- 
izing. The iron ore, which is black and opaque, is abundant, occurring in 
well-defined more or less angular grains. 
The rock is perfectly massive and possesses a typical "ophitic" or "dia- 
base" structure, the plagioclase having the form of well-defined laths 
