1226 NEW YORK STATE MUSEUM 



approaching horizontally; but this White lime quarry thrust 

 has a plane surpassing horizon tality, dipping to the westward, 

 and we infer that since the formation of the thrust plane, the 

 entire region has been tilted toward the west, perhaps during 

 the formation of the Posttriassic geanticline of eastern New 

 York and the Connecticut valley. 



Conclusion 



Our interpretation of the Vlightberg structure is as fol- 

 lows. The main structural features originated in a sigmoid 

 flexure, with broad arch on the northwest and narrow 

 trough on the southeastern side, which was formed by orogenic 

 forces acting from the southeast. This sigmoid fold, instead 

 of being a typical Appalachian overfold toward the northwest, 

 is an under fold in that direction, in which the steeper limb of the 

 flexure was on the southeast side. It is now a compressed 

 underfold, with its synclinal trough broken through stretching 

 of the middle limb, and its anticlinal crest bulged up and 

 broken by longitudinal thrusts formed as a result of the con- 

 tinued tangential pressure acting on a mass of strata carrying 

 little if any superficial load. The Glory Hole vein is the eastern 

 limb of the synclinal trough of the sigmaflexure. The eastern 

 edge of the Middle and Level veins is the common or middle 

 limb of the flexure, which, through stretching, has been 

 broken from the lower edge of the Glory Hole vein, and shoved 

 far upward and over southeastward into its present position. 

 The longitudinal fault between the eastern and western anti- 

 clinal arches is a break thrust along the axis of a small syn- 

 clinal trough that formed, in consequence of continued com- 

 pression, on the broad summit of the original arch. 



The mass of the Vlightberg overthrust consists of the upper 

 layers of the crest of the arch, which have been displaced and 

 moved to the westward by the compression of the trough. 



The smaller minor thrusts have already been explained as> 

 having been caused by torsion movements. 



In the North hill we see a typical Appalachian overthrust 

 formed from a fold of which the steeper slope was toward the 

 west ; a condition the reverse of that seen in the Vlightberg. 



Some observations on cleavage were made, and we are satis- 

 fied that the more prominent cleavage of the different beds was 



