Basic Rocks of Northeastern Maryland. — Leonard. 159 
still in its early stages cores of pleochroic hypersthene mav yet 
be seen surrounded by secondary hornblende, but commonly 
the former mineral has entirely disappeared. More or less iron 
oxide separates out during the change and is scattered throoigh 
the mass in small grains of magnetite. 
The following analysis (V) of a fresh and typical web- 
steryte from Oakwood was made by ]Mr. W. F. Hillebrand, of 
the United States Geological Survey. The rock is a very 
coarse-grained aggregate of hypersthene and diallage. This 
analysis agrees very well with those given by G. H. Williams* 
for the two varieties of webstervte from Baltimore countv. 
Si02 53.21 MgO 20.78 
TiOo 26 K2O 07 
Zr02 trace Na20 11 
AI2O3 1.94 LigO trace 
V2O3 03(034) H2O below 105° C 14 
Cr203 20 H2O above 105° C 87 
Fe203 1.44 P0O5 trace 
FeO , 7.92 FeSof 03 (02 S)$ 
NiO, CoO 03 CO2 10 
MnO 22 CI undet. 
CaO 13.12 Fl undet. 
SrO none 
100.47 
BaO none Sp. gr 3.34 
PERIDOTYTE. 
This rock forms several small areas within the noryte-gab- 
bro belt and also occurs at one point along the border between 
this and the serpentine. The largest mass is one and a half 
miles northeast of Rising Sun, at the Mount Hope church. The 
area extends in a northeast direction and is less than one- 
Cjuarter of a mile long. The rock, which outcrops at numerous 
points, has weathered in such a way that it presents a very 
rough and pitted surface. Associated witli the peridotyte is 
some pyroxenyte and smaragdite rock. Another area of 
much altered peridotyte is found one and a half miles northwest 
of Rising Sun near the Oak Grove schoolhouse. Peridotyte 
occurs as a dike outcropping along the railroad just below 
♦Am. Oeol. July. 1890. p. 3.5. 
tSulphur oalfulated as FeS-, but exists as Dvrrhotite or other suiphkle 
solublp in II("1. 
tl'erliaps mainly pyrrhotite. 
