10 NEW YORK STATE MUSEUM 



east and west by fragile black shales with a somewhat slaty- 

 structure [see pi. 2]. 



Near the base of this slope, or from about 20 to 60 feet above 

 the level of 4th street, the surface of the rock appears in a well 

 glaciated area broken by postglacial faults, or at least by faults 

 which interrupt the glaciated rock surface. 



The strike of the sandstones and slates is here g° east of north, 

 and the glacial striae run up the bank on a course s. 21 ° e. The 

 dip of the slates is approximately 40 e., where not involved in 

 the abrupt curvatures of the folds. 



The faults here referred to occur, so far as my observations go, 

 altogether on the eastern side of the sandstone beds in the axis 



SL 



Fig. 2 Cross-section of the left bank of the Hudson south of the Poesten kill, in Troy, N. Y. 

 showing position of postglacial faults in relation to river bank 



of the syncline. A rough sketch of a portion of the faulted sur- 

 face is shown in figure 3, in which there is no pretension to 

 accuracy of measurement. 



Below the area shown in figure 3, there is an imperfectly shown 

 slip of 6 inches, the greatest throw I have measured in eastern 

 New York. The faults which traverse the area mapped meas- 

 ured, in the order in which they are encountered in ascending 

 the slope, 5, 1, 1.5, and from 2 to 5 inches. Thus within 30 feet 

 measured up the slope there is a drop of 12 inches to the west 

 on these faults. All of the faults observed at this locality are of 

 the reverse type, with a steep dip to the east and a downthrow 

 to the west. With one exception the faults are closely parallel 

 to the steep dip of the stratification of the beds, though it is 

 noticeable that there is a tendency of the fractures to depart from 

 the bedding of the fine, black, fragile, shaly beds. One break 

 extends practically at right angles to the bedding with an uplift 

 on the north [see pi. 3]. Two of the fractures shown in the 

 sketch converge southward and die out within the limits of the 

 exposure. The other principal faults are traceable to the edge 

 of the clay deposit. Their full extent in that direction is 

 unknown. 



