160 Wisconsin Academy of Sciences , Arts and Letters. 
are to be observed. The splintered fragments of hornblende and the newly- 
formed minerals become roughly oriented with reference to a plane of 
schistosity. (See Fig. 8.) Plate I is from 
a photograph of the wall of hornblende 
gneiss on the left bank of the Patapsco 
river opposite Ilchester railroad station. 
In the same region are found other 
younger intrusive masses which cut the 
rocks just described. The most import¬ 
ant of these is a porphyritic granite con¬ 
taining allanite-epidote intergrowths, 
and having dioritic facies resembling the 
diorites associated with gabbro. Isolated 
bosses of a non-feldspathic pyroxene 
rock and a coarse hornblende picrite 3 - Section of Hornblende-Gneiss 
r (Metamorphosed hyperstnene gabbro) 
(Cortlandtite) occur. Further, a coarse from Thistle Cotton Mills,ilchester,Md., 
showing peripheral granulation of feld- 
pegmatite is especially abundant in the spar, fraying out of hornblende, and 
, . . . , „ . J development of epidote with zonal 
neighborhood of Ilchester. structure. X50. 
In the course of a hasty reconnaissance in the Odenwald in Hesse, I was 
much impressed by the striking resemblance in characters of the rocks of 
that region and of the one just described. The porphyritic hornblende 
granites and diorites of the Birkenauerthal resemble more than any others 
that I have seen the Ilchester granite. In the vicinity of Burg Franken¬ 
stein on the Bergstrasse occur gabbros associated with dioritic rocks bear¬ 
ing much resemblance to the gabbro-diorites of Ilchester. The Ilchester 
Cortlandtite finds its representative in the Schillerfels of Schriesheim. The 
analogy might be carried further to include a pegmatite'and a basic pyrox¬ 
ene rock (Wehrlite) from the same general locality in the Odenwald region. 
EXPLANATION OF PLATE. 
Gabbro-diorite passing into hornblende gneiss. On left bank of Patapsco 
river, near highway bridge, at Ilchester, Md. The gabbro-diorite is seen 
on the left, passing by insensible gradations into hornblende gneiss to¬ 
ward the right. 
