1895. ] NEW YORK ACADEMY OF SCIENCES. 217 
flows. Vesicles, flow-lines and flow-breccia are very common, 
and the scattered phenocrysts are often broken and displaced. 
Spherulitic and. perlitic structures, trichites and skeleton crys- 
tals*are sometimes excellently preserved. The basic rocks are 
chiefly diabase, and are in part as late as the Etcheminian. 
Breccias and tuffs are very abundant. The alteration is not ex- 
cessive except in the tuffs, many of which are now unrecogniz- 
able. The massive rocks are completely devitrified but other- 
wise not much changed; schistose cleavage is marked in the 
more highly metamorphic areas, but is generally absent. 
The soda-granite is a quartz-anorthoclase rock with augite 
and hornblende as the dark silicates. It shows a very strong 
granophyric structure in the central part, but is finer grained 
and somewhat porphyritic towards the edges. 
The dyke rocks are all basic and predominantly diabase ; 
a number belong to the rare type of diorite-porphyrite. The 
latter is a panidiomorphic rock with feldspar, brown hornblende 
and subordinate quartz. The age of the dykes is probably pre- 
Cambrian,* excepting a few of different type from the rest. 
In concluding, I wish to express my acknowledgments to 
Prof. J. F. Kemp, for his assistance and advice in carrying out 
this study. I am also much indebted to my father, Mr. Go 
Matthew, especially as regards the details of local geology. 
GEOLOGICAL DEPARTMENT, 
Columbia College, April, 1895. 
DESCRIPTION OF PLATES. 
PLATE XII. 
Fic. 1. Spherulitie structure in red felsite-porphyry (apobsidian) from the 
Hammond River below Upham, N. B. This section shows under 
higher magnification well preserved trichites throughout both the 
spherulitic. and non- spher ulitic parts of the rock (See. Fig. 1, p 199). 
Spec. 664. Magnified 37 diameters. 
Fig. 2. Red felsite-porphyry (dirachy te), showing feldspar in three genera- 
tions ; large phenocrysts, small rod- like crystals and small grains 
not well bounded. ‘The glassy material has been changed to 
micro-felsite. The only other minerals are magnetite and second- 
ary limonite replacing in part one of the orthoclase phenocrysts. 
Ree 
Spec. 575. >< 42 diam. 
PLATE XIII. Z 
Fig. 1. Perlitie structure in red felsite-porphyry (apobsidian ) from Hammond 
River below Upham. The stippled part is microfelsite, which 
shows a flow-brecciated structure, the horizontal shading repre- 
* And hence any rocks that they cut would be still earlier. They are very abundant 
in the intrusive granites near the city, and chiefly on this account the age of the gran- 
ite was provisionally placed as pre-Cambrian. It seems well to make this point clear, 
as it has been mis-stated in a recent abstract of the article describing the granites. 
