. Annual report. New York State Museum; Science; Science. POSTGLACIAL FAULTS OF EASTERN NEW YORK 27 be of the reverse type, indicating compression. The direction of the throw must depend upon the attitude of the planes of struc- ture—stratification or cleavage, or both—along which the move- ment takes place. In stratified rocks which have been thrown into anticlines and synclines, and have been subsequently rather deeply base-leveled, it is probable that the continuance of the lateral pressure which gave rise to the folds would con- centrate the horizontal strain upon the cores of the syncline
. Annual report. New York State Museum; Science; Science. POSTGLACIAL FAULTS OF EASTERN NEW YORK 27 be of the reverse type, indicating compression. The direction of the throw must depend upon the attitude of the planes of struc- ture—stratification or cleavage, or both—along which the move- ment takes place. In stratified rocks which have been thrown into anticlines and synclines, and have been subsequently rather deeply base-leveled, it is probable that the continuance of the lateral pressure which gave rise to the folds would con- centrate the horizontal strain upon the cores of the synclines in such a manner as to cause successive boat-shaped layers of rock with their wedge-shaped cross-sections to rise upward. By reason of the inward dip of the strata about the synclinal axes the appearance of overthrust would appear in the slips which marked the movement, as shown in the accompanying theoreti- cal diagram [fig. 8]. Thus synclinal cores must have a tend-. Fig. 8 Diagram showing cross-section of a normal upright syncline with a rising core due to slipping of successive layers in the trough under lateral compression ency independently of resistant remnant beds in their troughs to stand above the general level or to give rise to upfolds in the horizontal newer strata which in certain districts lie unconform- ably upon them. Small faults of this nature may arise in folded strata without direct connection with those greater and more deep seated faults which appear so abundantly in eastern North America to have had their origin in the fracture and displace- ment of the crystalline Precambric terrane. It is worthy of note that the few instances of postglacial faults as yet reported appear to be everywhere associated with highly inclined strata. It is to be presumed that the same stresses are equally opera- tive in the regions of horizontal strata with consequent displace- ments which take the form of horizontal thrust-planes whose time of movement is not so readily
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