METAMORPHIC ROCKS. 
451 
Limestone of Westchester and New-York counties. 
This rock is abundant, and extensively distributed in the counties of New-York and West¬ 
chester. It is all associated with gneiss, mica and talcose slates, and with granite or horn- 
blendic rocks, and is interstratified or embraced as beds in these rocks. In color it varies 
through white, grey and clouded to black; in texture it is coarsely crystalline, granular, and 
perfectly compact; in composition, it varies from pure carbonate of lime to magnesian and 
ferrdmagnesian carbonate of lime, with variable quantities of earthy impurities ; in hardness, 
from a very strong stone, to one so friable as to be capable of being crushed to sand by pres¬ 
sure in the hand. 
This rock is of greater present as well as prospective value in the region of country where 
it is found, than any other, unless it be the granite, which may, in progress of time, become 
equally valuable. 
Limestone of New-York counly. 
This rock abounds in the north part of the island, and has been quarried to a considerable 
extent for marble, building stone, and for lime. (See Plate 30, fig. 7, to illustrate the posi¬ 
tion, and the surface occupied by this rock.) The length of the exposed limestone is about 
one and a half miles. It was first seen in place a few rods from the tavern one mile and a 
quarter south of Kingsbridge, on the road to Manhattanville, and may be seen along the road 
until after crossing the Spuytenduyvel creek at Kingsbridge. The rock has been called 
Kingsbridge marble, but it “ has been chiefly wrought for burning into lime, is mostly of the 
variety called granular limestone, and is so loose in texture, that after exposure for a time to 
the weather, it falls to pieces, becoming a kind of calcareous sand.” At the junction with the 
gneiss, “ and often for a considerable distance into the marble, it retains the structure of 
gneiss with the mineral matter of limestone; but where the matter becomes pure limestone, 
it lies in beds without stratification, or but obscurely stratified. 
“ At the southern limit of the limestone, where it is from fifty to eighty yards in width, and 
about one hundred yards west of the road, the strike is N. 30° E., and the dip vertical. It 
is flanked on both sides by gneiss, and as it continues northerly in the direction of the strike 
or bearing of the strata, it widens until it becomes from four hundred to six hundred yards in 
width, and from ten to thirty feet in height, forming a low ridge immediately west of the 
road, but east of the main ridge of gneiss which flanks the eastern shore of the Hudson, and 
which terminates at Tubby hook, about half a mile north of the commencement of the lime- 
ice in this pond attaches itself to the loose boulders in shallow water, and floats with them attached, and ploughs up the 
gravel before them as the ice is driven toward the shore in the spring. In this way they are brought annually nearer and 
nearer the shore, until they are pushed beyond low-water mark, where they remain. Many of these boulders weigh fifteen 
or twenty tons. They all seem to have come from one general direction, viz. northwest. Mr. Stephen Ryder pointed 
out the boulders and furrows, and gave the explanation to Prof. Cassels. 
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