METAMORPHIC ROCKS. 
463 
frosts for ages. A large portion of the hill south of the beach, and of the locality at the 
southeast end of the beach, is composed of serpentine rock, and it is not impossible that 
quarries of some value rnay be opened there. This is an interesting locality. The serpentine 
farther south on the neck of land is like that of Hoboken and Staten island. 
“ It was at one time supposed that the serpentine found here, from its beautifully variegated 
green color and its resemblance to the Italian verd antico, might be employed as an ornamen¬ 
tal marble. But a careful examination of the material proved that it was traversed by seams 
and cracks, which everywhere divide it into small masses. It is also penetrated by other 
minerals, which, however they may add to its interest for cabinet specimens, render it unfit 
for the uses to which marble is applied. In a similar bed in the town of Rye, other and more 
rare magnesian minerals are found. Chromate of iron, the ore from which the chrome yellow 
of commerce is obtained, is here often disseminated through the serpentine, as it is also, 
although less abundantly, at New-Rochelle. It is doubtful, however, whether at either locality 
it exists in sufficient quantity to answer any useful purpose.”* 
Recapitulation, and Theoretical Considerations. 
In describing the Metamorphic limestones of Dutchess, Putnam, Westchester and New-York 
counties, we have traced them in different localities through various modifications of texture, 
from the grey and semi-crystalline limestones associated with talcose slate and the sandstone 
of the Taconic system, to the perfect dolomites and white and grey crystalline marbles asso¬ 
ciated with mica slate and granular quartz rock, north of the Highlands; and to still more 
crystalline limestones associated with mica slate, micaceous gneiss, hornblende slate, hornblen- 
dic gneiss, hornblende rock, sienite and granite, south of the Highlands ; and in these latter 
limestones, we frequently find some mineral substances, such as serpentine, brown tourmaline, 
copper and iron pyrites, magnetic sulphuret of iron, mica and magnesian minerals, particularly 
where they are near to undoubted plutonic rocks. These have been traced within the bounda¬ 
ries of New-York, between Mount Washington in the southwest corner of Massachusetts, and 
the city of New-York. The same may be observed in tracing the rocks of the Taconic system 
eastwards, from Washington county into Vermont; from Rensselaer and Columbia counties, 
to the Hoosick mountains in the eastern part of Berkshire county in Massachusetts ; and from 
Dutchess, Putnam and Westchester counties, into Litchfield and Fairfield counties in Con¬ 
necticut. 
The same rocks are found in those three States on the eastern side of New-York, and I 
have examined them with some care. Prof. Hitchcock has well and correctly described those 
of Massachusetts, and he considers them metamorphic rocks,t but was not able to refer them 
definitely to any particular geological age,f and it could not be done by studying the rocks of 
Massachusetts alone. To Prof. Emmons is due the credit of first rendering it highly pro¬ 
bable that the limestone of Burlington in Vermont is the same as that which is marble in 
* Prof. Beck, Fifth Annual Geological Report of New-York, 1841, p. 12. 
t Final Geological Report of Massachusetts, 1841, p. 587. 
t Ibid. pp. 573, 581. 
