The ground‐water geochemistry of glacial drift and bedrock of selected areas of New England, New York, and Pennsylvania differs considerably among the areas as a result of differences in bedrock geology. The New England study area is underlain primarily by feldspathic rock, large areas of New York are underlain primarily by carbonate and terrigenous sedimentary rock and some evaporite deposits, and glaciated areas of Pennsylvania are underlain primarily by clastic sedimentary rock with minor carbonate rocks. Mean concentrations of most solutes are greatest in the New York area and least in the New England area. In New England, the ground‐water geochemistry results mainly from the reaction of CO2‐charged water with feldspar and other primary silicates. Water in the New England bedrock is more highly evolved geochemically than water in the drift, presumably as a result of its longer residence time. In the New York area, the geochemistry of water in both types of aquifers results mainly from carbonate‐ mineral dissolution. Water in most glacial drift and bedrock is saturated with respect to calcite. In some parts of New York, the dissolution of evaporite minerals has a marked effect on the water chemistry of the bedrock. In most of the Pennsylvania area, the geochemistry of water in both types of aquifers indicates that, although carbonate minerals are the principal reactants, their influence on water chemistry is less than in New York. In parts of Pennsylvania, chemical differences between ground water from drift and ground water from bedrock are attributed to a higher proportion of reactive minerals in the drift than in the local bedrock as a result of glacial transport.

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In many mechanical systems, the tendency of sliding components to intermittently stick and slip leads to undesirable performance, vibration, and control behaviors. Computer simulations of mechanical systems with friction are difficult because of the strongly nonlinear behavior of the friction force near zero sliding velocity. In this paper, two improved friction models are proposed. One model is based on the force-balance method and the other model uses a spring-damper during sticking. The models are tested on hundreds of lumped mass-spring-damper systems with time-varying excitation and normal contact forces for both one-dimensional and two-dimensional stick-slip motions on a planar surface. Piece-wise continuous analytical solutions are compared with solutions using other published force-balance and spring-damper friction models. A method has been developed to set the size of the velocity window for Karnopp’s friction model. The extensive test results show that the new force-balance algorithm gives much lower sticking velocity errors compared to the original method and that the new spring-damper algorithm exhibits no spikes at the beginning of sticking. Weibull distributions of the sticking velocity errors enable maximum errors to be estimated a priori.

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