234 Geology 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 geoloii;ists, 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 localiiies of small extent are 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 them 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 amons: primitive rocks in the adit to Southampton lead 

 mines in Massachusetts- See Index to the Gecdogy of the 

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

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

 ought to be 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 fool 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 tlie 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 with crystals of quartz. 

 Geologists who travel on the canal, are requested to notice 

 a remarkable circumstance in Schuyler's lock, respecting 

 the meeting of the layers fn the rock. They meet and 

 tuiite by sutures precisely like the bones of the human era- 



