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The chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff. In all, 101 different rivers, each draining a primary lithology, were examined across the United States, Puerto Rico, and Iceland. To minimize seasonal effects, only rivers with at least two years of data were used. Basaltic catchments were examined in the greatest detail. In a survey of Hawaiian Island watersheds, the average river chemistries could be related to the distribution of soil associations within each catchment. An analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium (ion exchange) control on cation ratios. Among different lithologies, unique weathering rate relationships were …