An unusual, laminated, spherulitic limestone with cherty layers forms part of a volcanogenic sequence in the Midland Valley of Scotland, 27 km west of Edinburgh. It preserves a cross section of the early Carboniferous terrestrial community. Microcrystalline silica laminae containing inclusions of calcite or dolomite may be primary, and support a hot-spring origin for the deposit. Oxygen isotope analyses of the silica and carbonate are consistent with the precipitation of silica from hot, possibly boiling, hydrothermal solution. Such hot spring waters were presumably heated by hypabyssal intrusives associated with the West Lothian volcanic center, only 5 km to the northwest....