GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 29 



Matteawan, and the rock which carries it in these different locaHties 

 is often of very similar mineralogy and appearance in other 

 respects. 



Interpretation, The Matteawan inliers connect the Glenham belt 

 with the Highlands in a very satisfactory way. Other field relations 

 which are cited above, show that the rocks composing these inliers 

 are of Precambric age. The banded gneisses seen in the section 

 on the Wappinger Falls road across the Glenham belt, bear strong 

 resemblance to many of the gneisses outcropping in the town of 

 Matteawan along the base of the mountain. The hornblende gneiss 

 in places is identical with those occurring on the road from Brincker- 

 hoff to Johns ville across the Honness spur. When the dip may be 

 observed in the gneisses along the Wappinger Falls road, it is prac- 

 tically the same as that of the .Highlands rocks. The essential 

 identity as to the age and fundamental likeness in mineralogy and 

 relations of these inliers with the Highlands is almost certain. 



The character shown by the rocks which make up so much of 

 these inlying masses, and upon which most observers liave dwelt, 

 apparently admits of ready interpretation. 



During the time the early Paleozoic sediments of this region were 

 being laid down the sea was progressively transgressing upon and 

 overlappi g the old land mass from which its sediments were de- 

 rived. This old land mass would doubtless have become decayed 

 for moderate depths beneath the surface, or at least would have 

 suffered some changes in the minerals composing the rock. Where 

 subaerial disintegration actually took place, its products may have 

 remained undisturbed in favorable places, and it is possible to 

 imagine unat they were finally covered by the advancing waters 

 vithout having been much sorted. In other cases they would have 

 been washed away, leaving only the firmer rock, which probably, 

 however, had undergone some mineralogical changes, such as the 

 alteration of its ferromagnesian mineral. In other instances the 

 disintegrated rock would have undergone partial sorting. In other 

 cases it would have been completely sorted and a pure sandstone 

 formed. In some places the advance of the sea would have been 

 rapid enough to leave most of the material unsorted and only a 

 superficial layer of partially sorted stuff. All would probably 

 have been covered finally by a thoroughly worked over quartzitic 

 sand that deepened offshore as the sea advanced. 



In the process of time burial in itself would have brought some 

 changes in the subjacent altered gneisses; but the principal ones 

 would have been effected by the same processes that changed the 



