430 J. D. Dana—On Southern Westchester County 
The crystalline limestone—strictly dolomite—often contains 
so much dark brown or black mica in scales as to look like a_ 
thick-bedded gneiss; yet it betrays its true nature, here as 
usually elsewhere, by the occurrence of some crumbling sur- 
aces. Besides tremolite, chlorite, with a little graphite and 
coccolite-like grains. The white crystals accompany tremolite 
in northern New York, near the King’s Bridge Road,* and the 
coccolite variety characterizes part of the limestone of the 
“Mount Eden” region, north of Fleetwood Park. Orthoclase 
in cleavable pieces also is sometimes an impurity of the lime- 
stone; and pyrite is a common source of disintegration and 
iron-rust stains. 
The limestone areas are in part low and marshy, owing to 
the easy destruction of the rock. But in some parts of the 
region there are long, broad ridges, a hundred feet or so in 
height. One of these ridges extends from Morrisania to Ford- 
ham, and many quarries have been opened in it. Another 
of them, equally prominent but of the less pure, gneiss-like 
limestone, passes through “ Mount Eden,” and has given occa- 
sion to the extravagant expression Mount in the name of this 
locality of prospective streets and houses. 
After these general remarks, I proceed to the special facts 
connected with the limestone areas and the associated schists. 
1. Limestone Arn, No. 1. 
A. The portions of the Area in Westchester County.—The 
general fact has been stated that, in this easternmost of the 
belts, the beds on the eastern side have a high eastward 
the dip (figure 29), and on the western usually a high 
ans westward dip, corresponding with the idea that the 
AW beds make an anticlinal flexure. This steep dip 
_“_—_ continues on the eastern portion quite to the Harlem: 
but on the western, it varies in its northern part to 70° E., an 
south of Tremont station from 80° W. to 60° W., becoming 50° 
W. and less in local folds. : 
The center of the belt from Fordham to Morrisania, where it 
commences to widen, has equally high dip; but south of this 
e Road. 
The specimens from this locality were’ first recognized as pyroxene by the 
Abbé Haiiy, after an examination of crystals sent him by Dr. Archibald Bruce, 
the editor of Bruce’s Mineralogical Journal. The fact is reported in the last num- 
ber of that Journal, published in 1814, on page 266. 
