LInmestone Belts of Westchester County, N. Y. 199 
triclinic. Hornblende and augite are sparingly present. The 
rock is therefore a micaceous variety of the soda-granite. But 
though ordinarily massive, it sometimes has distinct indica- 
tions of bedding. The rock is most common in the vicinity 
of limestone belts. It occurs at Centerville, east of limestone 
number 4 (see map), and also north of this limestone in the field 
west of the road, where it is conformable with the limestone. 
K. The Chrysolitic rocks.—The chrysolitic rocks of the region 
have no resemblance in aspect to ordinary chrysolitic volcanic 
or igneous rocks. The kinds are (1) chrysolitic hornblendyte, (2) 
chrysolitic pyroxenyte, (8) chrysolitee noryte ; and these graduate 
not only together but also into a rock in which chrysolite is 
the chief constituent. They are black or brownish-black 
ua The chrysolite is more or 
less altered, as is shown (when examined in thin slices) by the 
bordering and intersecting bands of magnetite and viridite, 
and in some cases it appears to be changed to serpentine.” 
These rocks are largely exposed along the western half of 
the north side of Stony Point, west of the boat pier (the area 
is lettered zz’ on the map), and over Montrose Point, as we 
in its vicinity ; at which places they are associated with noryte 
southern Cortland. The most eastern locality observed is 
within half a mile of the eastern border of the town, near the 
middle of the three “emery” mines referred to beyond, and 
the most southerly, a short distance east of Croton, within half 
a mile of Croton River. 
e chrysolitic rocks are the most decomposable of the series, 
and wherever the brown-black ledges are crumbling in an 
extraordinary way and making a profusion of brown sand or 
rown or red earth, the presence of chrysolite may be suspected. 
FB. Iron and Emery Mines.—This Cortland region has its 
mines of magnetite, some of which are also mines of emery. 
The containing rock is either noryte, dioryte, or soda-granite, 
"' These chrysolitic rocks usually have, on a fresh fracture, the cleavage sur- 
faces of the hornblende or augite spotted with chrysolite; but the presence of 
chrysolite, however abundant, cannot be made certain without slicing for micro- 
spots on hornblende may 
If the cleavage of the hornblende has an unbroken surface it is probable that the 
rocks Mies no chrysolite. The hornblendyte has much stronger luster than 
