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NEW YORK STATE MUSEUM 



12 to 15 feet apart, converge toward the surface of the ground. 

 Their effect is to produce a quartet outcrop of the Stromatopora 

 bed of the Manlius limestone, and greatly to increase the ap- 

 parent thickness of the latter formation. There has been little 

 crushing along these minor thrust planes, and a shear zone of 

 only T \ to 1 inch thickness can be distinguished; but, neverthe- 

 less, the opposing faces of rock have well developed slickenside 

 surfaces. Close faulting with almost no shear zones is on the 

 whole characteristic of the dislocations in the limestones of this 

 region. These minor thrusts are very similar to some of those 

 figured by Sir Archibald Geikie, 1888. 1 



The formation of these minor thrusts was probably imme- 

 diately consequent on the plication of the anticlinal arches, and 

 their origin is assigned to torsion forces that buckled the anti- 

 clinal arch. 



A most interesting feature of the eastern anticlinal is the 

 pair of approximately parallel tranverse thrust faults of north- 

 easterly dip that transect the anticlinal arch and cut it into 

 three segments. Little trace of these two faults can be distin- 

 guished on the surface of the ground, but they have produced 

 important complications of the underground cement veins. The 

 Taylor's corner vein, after having been worked out across the 

 entire width of the anticlinal arch, finally dipped toward the 

 northeast, its foot wall flattened, and the farther edge of the 

 vein was truncated by a northeasterly dipping thrust fault 

 which afforded a hanging wall of Champlainic sandstone. The 

 southern end of the Middle quarry has a higher elevation than, 

 and actually overlies the broken end of the Taylor's corner vein, 

 and it, in turn, at its northeastern end dips steeply and is cut 

 off in similar manner by a thrust plane. Beyond this second 

 thrust plane the same vein is being worked at a higher altitude 

 in the south end of the Level workings. These transverse 

 faults are all overthrusts from the northeast, and in conse- 

 quence of their presence the segments of the eastern anticline 

 have been "telescoped," so that they overlap each other after 

 the manner of a vertical row of earthenware tiles on a roof. 



1 Recent Work of the Geological Survey in the Northwest Highlands of Scot- 

 land. Quar. Jour. Geol. Soc. London, v. 44, fig. 4-21. 



