110 J. D. Dana— Origin of the Rocks of the Cortlandt Series. 
mostly uncrystalline limestone 80 feet long and a foot or more 
wide in the chrysolitic rock of Montrose Point indicates a tem- 
perature of metamorphism much below that of fusion. 
3. Source of the material of the original beds. 
quartz. 
The three supposable sources of such characteristics are— 
(1) Detritus from the Archean Highlands. 
(2) Igneous eruptions, affording volcanic or igneous debris, 
in addition to ejected liquid rock, and along with more or less 
Archean detritus. 
(8) Detritus from the Highlands, supplemented by ingre- 
dients from the ocean. 
1. ARCHHAN DETRITUS. 
agnesian as well as ferriferous sediments might therefore 
have come from such a source; and the frequent occurrence 0 
hornblende schist in regions of the ordinary metamorphic rocks 
of Westchester County shows that their formation is nothing ex- 
ceptional. A feeble proportion of free quartz, as in the Cortlandt 
rocks, is not an uncommon fact. It characterizes muds or 
clays which have lost their quartz for making sand-beds 1m 
the separating process of wave-action or water-movement, an 
- it is exemplified in much hydromica schist, which often con- 
sists of hydrous mica alone, with little, if any, free quartz 
Again, the soda-lime feldspar, oligoclase, occurs in the granite 
and gneiss of the LR and, in fact, is common in these 
rocks wherever found, though in general subordinately to or 
thoclase; the Cortlandt rocks are peculiar only in the much 
larger proportion of soda-lime feldspars. In the Archean of 
the Adirondacks, labradorite rocks, closely like the noryte and 
