OBSERVATIONS ON THE STRUCTURE AND GEOMORPHOLOGY OF THE MINNEWASKA INLIER, MINNEWASKA STATE PARK AND MOHONK PRESERVES, NORTHERN SHAWANGUNK MOUNTAINS, SOUTHEASTERN NEW YORK

The inlier at Minnewaska formed when an anticline (trending N25E) in the Shawangunk conglomerate (medial to late Silurian) was breached by glacial (Wisconsinan) action exposing slightly deformed late medial Ordovician shales and siltstones of Martinsburg (Bushkill) aspect. Regionally the Shawangunk overlies the Ordovician strata with angular unconformity (Taconic). The contact within the inlier is covered by drift or scree. The inlier is subtriangular with north and west sides bordered by low cliffs. Southeast, the third side is rarely exposed. Overall dimensions are about 6,000 by 3,000 feet (1800 by 900 m). The crest of the asymetric anticline plunges gently to the northeast with subparallel limbs inclined 62° to the southeast and 17° to the northwest. At the latitude of the inlier, the wave length and amplitude of the fold approach 5000 and 300 feet (1500 and 100 m) respectively. Scattered outcrops of Ordovician strata are centered in an area about 3000 by 1000 feet (900 by 300 m). Five exposures projected into a northwest-southeast section suggest an anticlinal and synclinal fold striking north to northeast with limbs rarely inclined greater than 15 degrees. The wave lengths and amplitudes of these folds approximate 1000 and 100 feet (300 and 30 m) respectively. Relief within the inlier is about 320 feet (100 m). Erosion of the Ordovician strata is generally less than 200 stratigraphic feet (60 m). At the bases of most marginal cliffs there is a fringing skirt of large block scree resting on rounded boulder till. Angular blocks of Shawangunk scree seem to have been lowered on a melting stagnant ice surface rather than to have been directly deposited as rock fall. Unlike the rock scour basin at Lake Mohonk and the ice plucked depression at Lake Minnewaska, the Minnewaska inlier is a relatively positive feature within its Shawangunk confines reflecting its original anticlinal morphology.