140 
I Assembly 
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 Green- 
wood 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; some- 
times betioeen 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 dis- 
tant from each other. It is generally quite narrow, and occasionally it 
is cavernous. Its bearing is southwest and northeast. Its prevailing 
colours are white and red; much of the red is flesh red, and coarsely 
crystalline, forming a handsome calcareous spar. It every where con- 
tains imbedded minerals; those which particularly distinguish it in al- 
most every locality, are what is believed to be the boltonite of Shepardj 
and small black spinells. What I suppose to be boltonite, has hitherto 
been called brucite, which it resembles in some respects. The Minera- 
logist of the Survey will determine to which species it belongs. This 
rock also contains beautiful pargasite, sahlite and coccolite; also crys- 
tallized augite, scapotite, zircon and sphene; also serpentine and plum- 
bago. 
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 im- 
bedded crystals of hornblende. 
Three others are visible at the Duck Cedar pond, one of them finely 
exposed. It is here seen cutting the limestone precipice perpendicularly 
downwards fifty feet, and running nearly cast and west. The trap rock is 
perfect green stone. 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 attention. 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 gra- 
nite. This space is spanned by the lime rock. The water, at present. 
