234 



Otology of the Highlands 



not been thoroughly searched out. One object of this essay 

 is, to furnish to the industrious mineralogist those landmarks 

 which an outline of the rocks may afford. 



We found no well characterized mica-slate in the High- 

 lands. But the gneiss becomes more slaty about half a mile 

 north of Fort Montgomery, which is four and a half miles 

 south of the Military Academy. It would probably be cal- 

 led mica-slate by some geologists, though it always contains 

 a considerable portion of feldspar. It is highly ferruginous, 

 and tends rapidly to a state of disintegration. It seems to 

 contain considerable soft granulated sulphuret of iron. Sim- 

 ilar localities of small extent arc found near the Military 

 Academy. Blocks of this variety are laid in the walls of 

 some of the public buildings, which are soon disintegrated ; 

 staining the walls before ihem of a yellow ferruginous 



hue. 



We discovered a vertical layer of a slaty rock set in the 

 gneiss rock, which is, in all respects, similar to gray wacke 

 slate. It is firmly set in the base of the Dunderbergh hill, 

 on the east side of the river. A layer considerably resem- 

 bling this, though not quite so well characterized, is to be 

 seen among primitive rocks in the adit to Southampton lead 

 mines in Massachusetts See Index to the Geology of the 

 Northern States, 2d Ed. page 20 ; and American Journal 

 of Science, Vol I. page 136, Such anomalous formations 

 ought to he attentively studied. 



The transition rocks bounding the Highlands on the north 

 and south, bear a strong resemblance to the range of a simi- 

 lar formation along the western foot of the Green Moun- 

 tains of Vermont and Massachusetts. Maj. Rensselaer 

 Schuyler having transported vast quantities of the metallife- 



rous lime stone rocks from Barnagat, near the north side of 



the Highlands, for building the great sloop lock in Troy, I 

 had a very favourable opportunity for examining it. It is of 

 a bluish-gray colour, somewhat granulated, and often trav- 

 ersed by veins of white calc spar. It is often cellular, 

 and contains numerous geodes, lined witli crystals of quartz. 

 Geologists who travel on the canal, are requested to notice 

 a remarkable circumstance in Schuyler's lock, respecting 

 the n^eeting of the layers in the rock. They meet and 

 unite by sutures precisely like ihe bones of the human era- 



1 



. [ 



