1895. ] NEW YORK ACADEMY OF SCIENCES. 215 
An analysis of the diorite porphyrite, spec. 603, gave the fol- 
lowing results : 
Si O, 48.98 
EOF 0.56 
ENS Oy 17.76 
Fe, O; 2.14 
Fe O 6.52 
Ca O 8.36 
Mg O 2.09 
Na, O 6.77 
K,0 2.08 
Fixed CO, 0.82 
Loss on ignition 4.50 
100.58 
I am not aware that this rock has been reported before from 
North America. 
DIABASE. 
It seems very likely that this group of dykes is connected 
with the great surface flows underlying the Cambrian slates, and 
of “ Huronian” age. There is a great variety in their character, 
the majority being normal diabase, but many having the feld- 
spar in two or three generations, and some showing porphyritic 
augites. 
The normal diabase has a colorless or almost colorless augite, 
well twinned feldspar rods and magnetite in small. irregular 
grains. It is usually considerably altered, the augite being 
either uralitized or chloritized. In about half the dykes green 
hornblende, uralitic or compact, has entirely replaced the au- 
gite, still retaining the outward form of the original mineral. 
Some of the diabases are quite porphyritic, the plagioclase 
phenocrysts being short and stout, the groundmass containing 
small twinned rods and sometimes apparently a third genera- 
tion. These appear to be more feldspathic than the rest. 
Contact action has not been noticed except on the limestones. 
These are bleached by even small dykes for about 3 or 4 mm. 
from the edge; and in the case of a fifteen foot dyke near 
King’s Mill, Fairville (spec. 63), there is a development within a 
few millimetres of the edge, of epidote, titanite and pale green 
hornblende of tremolitic habit— and ¢ very pale green, a color- 
less. These constituents entirely replace the lime just along the 
contact. The diabase itself has the usual contact character. 
A single dyke (7) in the lower Coastal rocks west of the Cold- 
brook Marsh shows a departure from the ordinary type enough 
to merit special notice. It is rather coarse-grained, the mag- 
