No. 104.] 177 



liug turnpike. The gneiss is conformable in strike and dip with the 

 micaceous schists of the mountain on the east; and in some of the 

 outcrops these widely-marked and t\'pical rocks are within thirty 

 feet of one another. The schist makes up the crest of the mountain; 

 the gneiss forms a western and lower ridge of the same general range. 

 And it is first south of Poughquag that the gneisses rise to a height 

 equal to that of the schist ridges. 



South of the Beekman and Pawling road this geological boundary 

 has a south-west course to Whaley pond, which lies in a depression, 

 marking the limits of two diverse rock systems or terrains. From the 

 south-east side of the pond and where the railroad comes to the water's 

 edge, the line of division goes, first, easterly for a short distance, then 

 on a south-east course, east of the Whaley pond and Reynoldsville road, 

 to the Putnam county line. The mica schist, more or less garnetifer- 

 ous, makes up the most of the ridge west of the Pawling-Patterson 

 valley and approaches close to the outcrops of the gray, fine-crystal- 

 line biotite gneiss near the bottom of the hill and near the N. Y. & N. 

 E. R. R. line. They are so close in places as to exhibit the structural 

 relations with certainty. Crossing into Putnam county the course of 

 the boundary is south for two miles, being one mile east of Ludington- 

 ville and following the lower part of the western slope of the Iron hill 

 range and near the middle branch of the Croton river. From this 

 valley it bends south-east around the southern end of Iron hill; and 

 then has a north-east course nearly to the village of Four Corners, 

 where it again takes a turn to the east and east-south-east and is also 

 the south limit of the Patterson limestone valley thence to Towner's 

 station on the Harlem railroad. The exact location of the line across 

 the narrow valley, followed by the Harlem railroad, is difficult, on ac- 

 count of the drift and more recent formations which cover the rocks. 

 It is possible that the limestone of the Patterson valley stretches south 

 as far as the Croton lakes, but beyond that the gneissic rock outcrops 

 extend quite across the valley. The boundary may run southward, 

 following the contour of a limestone tongue as far as this lake, or one 

 and a half miles south of Towner's station. Or it may run in a direct 

 easterly course across by this station. East of the last-mentioned place 

 the line has a more tortuous course, going first north-east, then north 

 for a half a mile, around a rocky hill, west of Couch's Corner; thence 

 east and east-south-east, at the northern base of the rocky ridges 

 which rise up at the southern border of the great swamp. Haines' 

 Corner is near the limit northward of the gneisses. East of Iluines' 

 Corner the alluvial deposits of the Croton river valley conceal all the 

 older strata and make the location doubtful. Passing over this strip 

 of alluvial and drift deposits the eastward extension of our lino is ]>ut 

 in the Quaker brook hollow, which is a deeply wooded valley, having 

 the high schistose-rock hills of north-east Patterson on the north 

 and the harder-grey gneisses on the south. 



This valley appears to have been worn down in the softer schists at 

 their junction Avith the gneiss. It is a topographical as well as a geo- 

 logical feature. The boundary Ime, as thus traced, crosses into Con- 

 necticut near the head of this Quaker brook hollow. Between 

 Towner's station on the north and Brewsters at the south, the east- 

 ward extension of the Highlands Archaean has a breadth of six miles, 



[Assem. Doc. No. 104.] 23 



