J. D. Dana—Origin of the Rocks of the Cortlandt Series. 105 
ern and southern limits, only ingredients occurred for making 
common mica schists and gneisses with subordinate layers of 
hornblende schist ? 
Before proceeding to this topic I will first mention the facts 
as to the special geographical position of the area covered by 
the Cortlandt rocks; and, secondly, briefly review the evi- 
dence as to their metamorphic origin. We shall then be pre- 
pared to enquire into the source or sources of the material. 
1. Geographical Position of the Area. 
The small region of Cortlandt rocks is situated in the vicin- 
ity of the Hudson, near where this river leaves its channel 
through the Archean Highlands. This relation to the posi- 
tion of the Archean and the river channel is shown on the 
following map (p. 106). Upon it, the Archzean area is the 
black portion dotted with small vs, crossing the Hudson, from 
southwest to northeast, between Moodna and Fishkill on the 
north and Peekskill on the south: and the Cortlandt rocks 
occupy the area east of the Archean, south and southeast of 
Peekskill on the east of the Hudson, and on Stony Point (S 
on the west side of this river. Near Peekskill the Cortlandt 
area is separated from the Archean by belts of limestone (hori- 
zontally lined on the map), quartzyte, argillyte-like hydromica 
schist and mica schist, in all one to three miles in width; and 
that of Stony Point has, between it and the Archean, a contin- 
uation of the same rocks (the limestone area on the map being, 
as elsewhere, horizontally lined, and that of the slates, Shih are 
partly quartzyte, distinguished by a vertical lining with white 
and dotted bands). The portion of the map north of the Ar- 
chean and occupying valleys within its area, has been already 
explained as Lower Silurian; (1) limestone, (2) slates or schists 
(vertically lined), and (8) quartzyte (dotted), the limestone 
and schist in places fossiliferous; and as part of the great for- 
mation which comprises and is continuous with the true Ta- 
conic schists and limestone to the northeast, and the recog- 
nized Lower Silurian rocks of New Jersey and the States 
to the southwest. 
