Basic Rocks of Northeastern Maryland. — Leonard. 155 
The formation of hornblende from pyroxene is by no 
means uncommon and the alteration need not be described here. 
DIABASE. 
At several points between Rising Sun and Sylmar station, 
on the state line, boulders of diabase were found. These 
doubtless belong to the dike described by H. C. Lewis and 
traced by him as far as the Maryland line which it crosses prob- 
ably a little west of Sylmar.* The dike extends in a southwest 
direction through southeastern Pennsylvania, where it was 
followed for a distance of seventy miles. The width at some 
points was found to be one hundred feet. Its age is thought by 
the above writer to be late Triassic, since it cuts rocks of the 
latter age. 
Diabase boulders are quite abundant just across the rail- 
road east of Rising Sun and south of the wagon road ; they are 
also found in the fields south of the railroad at other points 
between here and Sylmar. G. P. Grimsley states that a diabase 
dike was traced for nearly a mile south of the town of Liberty 
Grove. Since these scattered boulders are in general arranged 
along a line having a northeast-southwest direction and extend- 
ing from the state line to the vicinity of the town above men- 
tioned, the evidence seems to be sufficient to warrant the repre- 
sentation of it which has been made upon the map. 
The rock is a fine-grained diabase which has a metallic ring 
when struck with the hammer. The weathered surface is cov- 
ered with a thin coating of red clay. Under the microscope the 
rock is seen to be composed of lath-shaped crystals of feldspar, 
irregular grains of augite and a little magnetite. 
PYROXENYTE. 
With a decrease in the amount of feldspar the noryte and 
hypersthene-gabbro pass over into rocks composed wholly of 
pyroxene. These pyroxenytes are common at many points 
along the border next the serpentine, where they are closely 
associated with the latter rock and also with the peridotyte. 
Intermediate types between the pyroxenyte and noryte are 
often found. Among the localities for the pure pyroxene rock 
may be mentioned the following: in the vicinity of Oakwood, 
especially just east of town at the Mount Pleasant academy ; 
♦Proc. Amer. Phllos. Soc, May 15, 1S85, pp. 438-456. 
