12 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 
the first generation, while feldspar, augite, and biotite crystallized nearly 
contemporaneously and form the second generation. The secondary 
minerals are uralite, chlorite, biotite (in part’), leucoxene, kaolin (%), 
magnetite (in part), calcite, pyrite, and quartz. The plagioclase is 
somewhat variable in composition, owing to zonal structure, but has 
probably an average composition corresponding to andesine. It is also 
probable that orthoclase is present, though the potash obtained in the 
analyses may be derived from a plagioclase containing a considerable 
per cent. of potassium. The augite-diorite differs from the diabase in 
that the ophitic structure is wanting, and that the brown hornblende, 
which now comes into greater prominence than the augite, is generally 
in idiomorphous crystals. The diorite is characterized by very perfect 
instances of the parallel intergrowth of augite and hornblende. 
In both the diabase and diorite the change of the augite has been 
uralitization, though in the diorite it has in many cases changed directly 
to chlorite. 
In conclusion, I have to acknowledge obligation to my instructors, 
Mr. J. E. Wolff, of Harvard University, and Dr. George Huntington 
Williams, of the Johns Hopkins University. The greater part of the 
microscopical examination in connection with this paper was made in the 
laboratory of Mr. Wolff, and I am indebted to him for much advice and 
suggestion. Dr. Williams has examined most of the slides, and assisted 
me in countless ways in the preparation of this paper. I am also much 
indebted to Mr. R. C. Sweetser, of the Worcester Polytechnic Institute, 
for a complete chemical analysis. 
NovEMBER, 1887. 
EXPLANATION OF PLATE, 
Fig. 1. Illustration of the change of hexagonal plates of biotite to chlorite, with 
separation of magnetite in concentric rims. From sections No. 202 
and 203. 
Fig. 2. Illustration of the intergrowth of augite and brown hornblende, and 
alteration of the former to chlorite. The alteration of ilmenite to leu- 
coxene along the Gleitfldchen is also shown. From sections No. 202 
and 208. 
