Data are presented on daily fluctuations of soil pH in organic soils overlying Carboniferous Limestone in Co. Clare, Eire. High rainfall leads to a drop in pH, as acid waters percolate through the soil, but after rainfall the solution of carbonates in the soil or the solution of the bedrock leads to a return of soil pH to alkalinity. Carbonates tend to remain in the soil on poorly drained sites but solutional removal of calcium occurs on freely drained sites and in the latter case the return to alkalinity is not so rapid. The presence of Calluna vulgaris is thought to be important as it appears to increase the acidity of percolating soil waters. On freely draining sites bedrock erosion may progress to such an extent that deep runnels form, down which soil may be lost.