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NEW YORK STATE MUSEUM 



slates on the east of the great fault. This writer makes no 

 mention of these recent displacements in the work referred to, 

 published in 1904. It is to be noted that the postglacial faults 

 at Defreestville are vertical at least at the present surface of the 

 ground, a fact which does not preclude their belonging to the 

 class of reverse faults due to compression. 



Faults at Copake. The fractures in Copake are to be seen at 

 the road corners ^4 m ^ e south of the Central New England Rail- 

 road station. Altogether the exposures of the phenomena at 

 this locality constitute the most instructive assemblage of these 

 small fractures which the writer has seen. It is stated above 

 that this is probably the locality originally found by Mather. 

 The slates, lying within the area mapped as Cambro-Siluric 



Fig. 4 A cross-section of the postglacial faults in the vertical slates at Defreestville, N. Y. 

 The slight westward inclination of the road is neglected in the profile. The fourth fault from 

 the right is assumed to be .25 inches throw in the table. The oblique lines in the diagram stand 

 for shading only. 



limestone on the State map of 1901, are exposed along the eastern 

 side of the main road from Copake to Boston Corners for several 

 yards north of the crossroads and as well on the west side of 

 the main road in the crossroad. 



The following very detailed measurements were made at this 

 locality with the view of determining precisely the rate of dis- 

 placement for a given horizontal distance, for in this way only 

 can the throw for the belt of fracture be determined. The first 

 measurement was made from right to left across the area north 

 of the crossroads shown in the photograph [pi. 4]. A tape meas- 

 ure divided into feet, inches and quarter inches was laid over 

 the surface of the road at right angles to the structure with the 

 zero end of the tape on the east in each case. The surface of the 

 rock inclined very gently to the west but no allowance has been 

 made in the distance for this departure from horizontality. 



