in the Wappinger Valley Limestone. 129 



or four jogs, as the belt widens to the west, until the field next 

 south of T. A. Hinkle's cottage is reached; from that point it 

 is nearly straight. Close to this line, at the distance of a few 

 feet throughout its entire length, there are many outcrops of 

 Hudson River shale which continue west to the Hudson River, 

 unless Utica shales may occur at some points. The shales are 

 in many places separated from the Potsdam limestone by lines 

 of springs and ponds, or by dry gullies. From the extreme 

 northern end, the plane of contact is marked by a line of ponds 

 nearly to Hinkle's house. Close to this house, to the west of 

 it, there is a deep gully, with the limestone on which the house 

 stands, on the east, and the shales, standing nearly vertical in 

 a bold exposure, on the west. This gully continues to mark 

 the line to the southwest as far as the turn in the Ferris road, 

 beyond which the demarcation is produced by a different but 

 no less striking plan ; for south of this point the limestone 

 remains a high conspicuous ridge, abruptly steep on the western 

 side, while the shales, mostly covered by drift, form a level 

 plain at its base. 



These facts make it evident that there is also a line of fault 

 between the Potsdam and the Hudson River shales at the 

 western margin of the limestone belt, more or less parallel to 

 the strike. The general direction of this line of fault is about 

 N. 40° E. The Potsdam strata near the line of contact are 

 generally deflected in such a way as to have less easting in the 

 strike, which is in such places from N. 4° E. to N. 11° E. 

 Thus at the extreme north end of the main fossiliferous hill 

 (A) the strike varies between the limits just given, while the 

 dip becomes as low as 20°. At the hill of calcareous quartzyte 

 in the third field south of the Driving Park (Hill F) the strike 

 is in some places 1ST. 11° E., and the dip 35°. 



On the other hand, the Hudson River shales incline to 

 acquire more easting in the strike, in the vicinity of the plane 

 of contact. In such cases they have quite frequently a strike 

 of 1ST. 46° E. (their general strike in the vicinity being about 

 N. 31° E.). They also, in such positions, are often found 

 inclined at a very high angle. These phenomena seem to 

 indicate considerable friction by a lateral motion in a north- 

 easterly and southwesterly direction, as well as in the upward 

 motion, at the time of the uplift of the Potsdam. This fault is 

 the more interesting, because it is evidently related to the 

 great fault described by Sir William Logan and Professor 

 James Hall as extending from Quebec to the Hudson River 

 near Rhinebeck. If, as has been suggested by Professor J. D. 

 Dana, this should more properly be regarded as a series of 

 more or less parallel faults, the present one would constitute 

 the most southern one of the series yet described. 



Am. Jour. Sci.— Third Series, Yol. XXXI, No. 182.— Feb., 1886. 

 9 



