250 
The American Geologist. 
October, 1896 
liiotite, of brown color, strong absor])tion. and cliaraeteris- 
tic form occurs in varying amounts. 
Feldspar is found in grains, at times showing the polysyn- 
thetic twinning of plagioclase. It sliows only slight evidences 
of strain, and occurs as a subordinate mineral, except at 27a 
and 27g along the edges of the dike, where it is the prominent 
constituent and gives the rock tiie more normal diorite ap- 
pearance. The axial angle at times is very small, giving 
almost the uniaxial cross of (piartz. Decomposition is not 
marked as a rule. 
Pi/roxe/te is present as an accessory mineral in light green- 
ish grains, with its usual large extinction angle, bright inter- 
ference colors and absence of pleochroism. 
Titanite is unusually developed in this dike. One very large 
crystal was noticed in 27c (Fig. 4). The crystals, of the com- 
mon wedge-shape habit, are nearly colorless and exhibit 
marked pleochroism. They compare ver}'^ favorably in size 
with the large yellowish red titanites, seen in the syenite of 
the Plauensehen Grund, Saxony. 
In some cases the titanite appears with cores of titaniferous 
magnetite. 
Pig. 4. Large titanite crystal (in the center of tlie section) and granular mixture 
of hornblende (hi, feldspar (f),biotite (b), pyroxene (pj and apatite (a). Dike 
No. 27. 
Apatite is seen in large grains in the basic portions of the 
rock, and in slender hexagonal prisms in the feldspar, for 
which the largerlgrains might easily be mistaken, except for 
the more markod relief and the uniaxial interference figure. 
