Foreland folds, sandwiched between unfolded strata, occur within a 2-m-thick zone in the Middle Ordovician Dolgeville facies, central Mohawk Valley, New York. These folds resulted from compression, believed to have been due to reverse (westward) tilting of the distal continental shelf and proximal slope of the western flank of the Snake Hill Basin and to have been caused by emplacement of gravity-slide blocks into Snake Hill basinal sediment during Orthograptus ruedemanni graptolite time. Supposedly, the added weight of the immense slide blocks depressed the lithosphere sufficiently to produce a rejuvenation of the Adirondack arch in the guise of geologically sudden westerly upthrowing of fault blocks. This produced a reverse tilting of the sea floor west of that arch. Some of the semiconsolidated or unconsolidated Dolgeville lime beds were thrown into serpentinous convolutions owing to this abrupt reversal of dip.