Byron D. Stone 1971 <p>The study-area lies in south-central New Hampshire, and is bordered on the west by the Merrimack River, the principal north-south drainage route of central New Hampshire. </p><p>The classical two tills of New England outcrop in the area. In a unique exposure of the sandy upper till, a loose ablation unit overlies a compact basal unit. Both upper till facies overlie a sheared section of dense, olive-gray lower till. </p><p>Outwash sequences mapped in the study-area are progressively younger to the north, indicating backwastage of the Wisconsinan ice sheet. </p><p>Primary structures in proglacial Lake Merrimack sediments include contorted bedding, buckled laminae, and folds. A large slumped section in lake sediments exhibits three distinct deformation zones, characterized by brittle, ductile, and unconsolidated deformation. Cross-cutting relationships establish four fold generations and a deformation sequence in the slumped section. Slip in each fold generation was along nearly parallel slip-lines, as deduced from analyses of fold rotation senses. </p><p>The primary and slump deformation features contrast sharply with the intense style of deformation of lake beds below till at an apparent ice readvance cut. The deduced drag fold slip-line agrees with till fabric point maxima and dip-slip on one group of thrust faults. A southerly movement of readvancing ice is inferred.</p><p>The study-area was deglaciated about 13,000 years ago, according to a proposed deglaciation model for New Hampshire. The model is based on Nye's theoretical glacier surface gradient, and evidence for active retreat of the Wisconsinan ice sheet.</p> application/pdf 10.3133/ofr71269 en U.S. Geological Survey Deglaciation events in part of the Manchester South 7.5' quadrangle south-central New Hampshire reports