GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE I9 



of the town of Matteawan. The discussion of these may be fol- 

 lowed by reference to the map of Matteawan (figure 8). 



The most western outcrop which has been noted is at the corner 

 of Vail avenue and Washington street. The gneiss at this spot 

 is very similar to that which composes the two inliers shown on 

 the map at the northwest. Another outcrop occurs at the junction 

 of Prospect and Mountain streets. A line drawn between these 

 two outcrops marks the western boundary of the gneisses of the 

 mountains, so far as they can be followed by actual outcrops. East 

 of Washington street along Prospect, Union, Robinson and Alice 

 thoroughfares and along Green, Park, Duncan and Goodrich side 

 streets, outcrops are numerous. North of Mountain street the 

 gneisses pass beneath the drift. A quarter of a mile to the north- 

 east they are exposed again in the gorge of Mount Beacon brook. 

 The reddish and greenish colors, characteristic of the Glenham belt 

 and the inliers farther west, and frequent epidotic gneiss, were noted 

 among the surface exposures of the gneisses just described. Other- 

 wise these exposures are similar to the rocks in the Mount Beacon 

 brook section. 



Mount Beacon brook section. Above and for a short distance 

 below the bridge on Mountain street, near the foot of the mountain 

 road, the brook has cut an interesting section in the gneisses. Just 

 above the bridge the foliation and " bedding " planes strike n. 54° e. 

 arid dip about 75° s. e. Below the bridge the strike varies be- 

 tween this angle and 69° e. of north. The rocks in this section 

 show an isoclinal arrangement in " beds '' with high dip to the south- 

 east. 



Below the bridge, the lowest portion of the section involves some 

 forty feet of dark hornblendic gneiss. This rock is banded, though 

 in places for the width of several inches it is massive. When water- 

 worn, such surfaces present a spangled appearance. This 

 " stratum " is abruptly succeeded by a lighter colored one of much 

 less uniformity of appearance. It is made up of imperfect alter- 

 nations of granitic, quartzitic and composite " beds," which vary 

 in thickness from the width of an inch or less to two feet. Some 

 '' beds " show light and darker bands. Others are uniformly light 

 colored, often with little or no trace of a ferromagnesian constitu- 

 ent. This '' stratum " continues up stream for a hundred feet or 

 more and passes beneath the bridge. It is succeeded by the Bald 

 hill gneiss with varieties that strongly resemble the rocks of the 

 Glenham belt and the Matteawan inliers in texture and mineralogy.. 



