THE GLACIAL GEOLOGY OF THE HUDSON RIVER GORGE BETWEEN ALBANY AND NEWBURGH, NY, BASED ON BRIDGE CROSSINGS

The Hudson River bridge crossings in the mid-Hudson Lowlands show bedrock strath terraces and overlying glacial and Holocene deposits. The elevation of the preglacial Battenkill-Hudson strath terrace ranges from +9 m at Cohoes to -10 m at Castleton. The Battenkill-Hudson hangs on the preglacial Colonie channel at the confluence at Ravena. The floor of the Colonie is at -45 m at the confluence, sloping to –65 m, with an inner gorge at -100 m at Newburgh. The overlying glacial deposits include Mohawk till, ice-contact stratified drift, Lake Albany silts, clays, and sand, Quaker Springs, Coveville and Fort Ann fluvial deposits, and Holocene alluvial and tidal deposits. The oldest glacial deposits are at Newburgh, where a thick gravel sequence was sampled consisting of Little Falls gravel (?), outwash from the Shenandoah ice margin and Middleburgh-Rosendale (M-R) readvance, and Lake Albany II, Quaker Springs, Coveville, and Fort Ann fluvial deposits. The outwash deposits extend north to Poughkeepsie, where they grade into boulder gravel deposited by the M-R readvance. The boulder gravel is overlain by Albany I and Albany II clays and Quaker Springs through Fort Ann fluvial deposits. The Quaker Springs through Fort Ann deposits can be traced to Albany. They are deposited on deeply incised Lake Albany I and II clays and Mohawk Till of M-R age. Late Fort Ann through Holocene tidal deposits are organic-matter rich muds that coarsen northward to a sandy tidal delta at Catskill.