METAMORPHIC ROCKS. 477 
rock, interstratified with the granitic and hornblende rocks, occupies a breadth of nearly or 
quite a mile, being wider than where seen at any other place. ^ 
“ From this point, it may be traced northeast by the way of Little Round pond, northeast 
corner of Bog-meadow pond, southwest by the way of Popelo’s pond, and the brook from the 
Two ponds to Greenwood furnace ; thence, with some interruption where it crosses the Ra- 
mapo, by the east side of Duck-cedar pond, to the New-Jersey line. 
“ In all this extent, it frequently disappears and again reappears, after having apparently 
been cut off by the granitic rocks. It is seen in some places only a rod, or even less in 
breadth. In many places it is seen in contact with the granite, the gneiss and hornblende 
rock; sometimes between them, sometimes above them, and sometimes beneath them. It is 
not stratified. In all this extent, which is about twenty miles in a straight line, it is confined 
between certain limits, and never appearing northwest or southeast of given lines, which may 
be about a mile distant from each other. It is generally quite narrow, and occasionally it is 
cavernous. Its bearing is southwest and northeast. Its prevailing colors are white and red ; 
much of the red is flesh-red, and coarsely crystalline, forming a handsome calcareous spar. 
It everywhere contains imbedded minerals ; those which particularly distinguish it in almost 
every locality, are what is believed to be the boltonite of Shepard, and small black spinelle. 
What I suppose to be boltonite, has hitherto been called brucite, which it resembles in some 
respects. The Mineralogist of the Survey will determine to which species it belongs. This 
rock also contains beautiful pargasite, sahlite and coccolite ; also crystallized augite, scapolite, 
zircon and sphene ; also serpentine and plumbago. 
“ A few trap dykes are seen cutting obliquely across this rock, one of them is partially 
exposed at the Two ponds in Monroe, and contains imbedded crystals of hornblende. Three 
others are visible at the Duck-cedar pond, and of them finely exposed. It is here seen cut¬ 
ting the limestone precipice perpendicularly downwards fifty feet, and running nearly east and 
west. The trap rock is perfect greenstone. A few rods from the southwest end of Popelo’s 
pond, where the stream enters it, this rock forms a perfect natural bridge. It is used as such, 
and one might cross it without being aware, unless the noise of the brook aroused his atten¬ 
tion. The breadth of this bridge across the stream is fifty feet, and its length up and down 
the stream seventy-five or eighty feet. Hornblende rock supports the arch on one side, the 
other is covered by soil, but it is believed to be granite. This space is spanned by the lime- 
rock. The water, at present, fills the concavity below, so that I could not see through ; but 
in times of drought, people pass through it. 
“ This limestone is also met with half a mile southwest of the Queensborough forge, very 
much resembling that at Fort Montgomery, and containing the same substances imbedded in 
it. It is here of very limited extent, being confined to a few small elevations of a few rods- 
in extent.”* 
A bed of limestone containing serpentine, was found in Rockland county. It is on the 
'Third Annual Geological Report of New-York, 1839, pp. 139, 141. 
