1893. | NEW YORK ACADEMY OF SCIENCES. 75 
series, and in the other related rocks from the well-known 
exposures uear Baltimore* and in northern Delaware.} 
C. E. Hall records also black boulders from the roadside 
toward Feasterville, and a number of other rocks from the 
neighborhood, whose microscopic description attracted my 
attention. Fortunately in the careful methods practiced by the 
Pennsylvania Survey, as regards their museum material, they 
were all recorded by numbers, and by the courtesy of Professor 
J. P. Lesley I have received some chips for thin sections. The 
‘* diorite ?’’ No. 5806, is an olivine-diabase, and undoubtedly a 
stray Triassic boulder. Ries and Fennor found one of much 
the same character (No. 16). It was only provisionally called 
by Hall ‘“‘ diorite?”’ His analysis is quoted below. No. 5309, 
called provisionally “syenitic gneiss?’ contains shattered 
quartzes, orthoclase and decomposed garnet. The dark silicate 
is too much altered for recognition, but it probably was horn- 
blende. Nos. 5305 (‘‘ trap ’’) and 5807 (“ black syenitic gneiss ”) 
are both formed of green hornblende in largest amount, with 
much less plagioclase. They are amphibolites rather than trap 
or diorite, and are doubtless much metamorphosed igneous 
rock of an original dioritic nature. They are very like our 
No. 8, which was gathered east of the quarry. The association 
of such rocks, with norites and gabbros, is known both at 
Baltimore and in Delaware. The analyses of two of the above 
numbered specimens yielded the following (5306 is by C. E. 
Hall, 5309 by F. A. Genth, Jr.): 
5306, 5309. 
Loss. 1.50 1.43 
Si0, 47.79 73.26 
TiO, 1.00 0.49 
P.O; 0.07 0.25 
CO, 0.57 : et Pe 
Al,0, 16.58 12.41 
Fe,0, 2.93 Wes" 
FeO 9.05 2.34 
MnO oweees tr. 
MgO 8.17 1.06 
CaO 9.33 1.23 
Na,O 2 20 2.68 
K,O 0.40 4.51 
99.69 101,19 
Sp. Gr. 2.689 
*G. H. Williams, Bulletin 28, U. 8S. Geol. Survey. 
+ F. D. Chester, Bulletin 59, U.S. Geol. Survey. 
