250 
ANNALS NEW YORK ACADEMY OF SCIENCES 
Manhattan on the lower east side. The most massive type is undoubtedly 
an intrusive. On account of its typical development in Long Island City 
the writer suggests the name Ravenswood granodiorite for the type. 
Inwood Limestone 
The Inwood is generally a very coarse-grained, crystalline limestone. 
The chief variation is in the presence of mica and chlorite flakes, which, at 
some points, become so abundant as to form calcareous mica or chlorite 
schist rather than limestone. This is especially true wherever shearing has 
affected the formation, as along certain fault zones, and where underground 
circulation has dissolved some of the lime, leaving the less soluble constitu¬ 
ents. In some cases of this kind'! the resulting residuary material bears no 
resemblance to the ordinary, typical Inwood. The genetic relations, how¬ 
ever, are seldom obscure even in the worst or most modified cases. 
Manhattan Schist 
The Manhattan is the most variable formation. Typically, it is a 
coarse quartz mica schist. The mica flakes are large and constitute the 
larger proportion of the rock in most cases. Quartz, however, is abundant; 
feldspar less abundant than in the gneisses. The rock is usually not banded 
but irregularly streaked and complexly crumpled with numerous lens-like 
developments of segregated quartz and other secondary minerals. In its 
most characteristic facies, biotite and a white, silvery or pearly mica is found. 
This pearly mica is probably the most characteristic constituent of the 
Manhattan formation. Its presence in any considerable amount makes 
identification reasonably certain. In the Manhattan, however, are numer¬ 
ous varieties of very different character, some of which are essentially identical 
with those occurring in the Fordham Gneiss. They are chiefly intrusive 
types and vein-like developments that occur as streaks or bands or masses 
of hornblende schist, granite, pegmatite and similar rocks. It is evident 
that whenever these types are the only representatives to be found, the 
identification is wholly uncertain. An additional variety is the serpentine 
and amphibolite or so called “anthophyllite,” but this has a limited dis¬ 
tribution and nowhere, so far as the writer is aware, leads to any confusion 
of identification. 
Many minor variations occur, and the change takes place rapidly, 
showing a great range in a single outcrop. In some places much epidote is 
developed, so that the rock is a typical epidote schist. It would be possible, 
on this account, to sub-divide these three formations into a considerable 
