J. D. Dana— Origin of the Rocks of the Cortlandt Series. 108 
Art. XIX. — Geological Relations of the Limestone me of 
Westchester County, New York; by JAMES D. Dan 
OrIGIN OF THE Rocks OF THE ‘* CORTLANDT SERIES.” 
e account of the cose Uh Cortlandt rocks* I rit 
a large part of them afford evidence of conformability to the 
associated schists and limestone strata of the country, as if one 
with them in metamorphic origin; and that if any were truly 
eruptive these were in part more recent than the limestone, 
since they cut through it at Verplanck Point. They hence 
present nothing against the chronological conclusion which 
has been reached. 
These rocks, however, are so limited in distribution, and so 
peculiar in composition—being often chrysolitic, always having 
soda-lime feldspar predominant, and containing little or no 
quartz—that it becomes an interesting question, Whence their 
ih interpolation among the schists and limestones of the 
region 
That the lithological facts may be in mind preparatory to 
ot following discussion I here re-mention the prominent kinds 
ro 
Soda-granite: granite-like, consisting chiefly of oligoclase 
sod biotite, with little quartz, and often ¢ ontaining some horn- 
blende; varying from coarse +s tine in grain, and very light-col- 
ored to black—the black very micaceous and fine-gr aine 
2. Dioryte, Quartz-dioryte: chiefly oligoclase and hornblende, 
with more or less aba and a little quartz; varying from very 
coarse and geet ike to fine-grained. 
iefly the feldspar, andesite—or, more probably, 
its equivalent, "| of labradorite and 2 of ee ae er- 
sthene, with more or less augite and biotite; usually dark gray or 
reddish brown in color, and rather finely granular; the hyper- 
sthene often in small crystals seldom — a sixth of an inch 
in length, and never. in folia. 
sometimes a grayis -green pyroxene, 
Tt Chrysolitic Ren aeceiti chrysolitic pyroxenyte, with 
some elke nory 
* This shngin for September last, ITI, xx, 1 
Am. Jour. Sor.—TuirD ing emma Vou. XXII, No. 128. eae 1881. 
