Delicate hollow spheroids (1 to 2 mm) composed of radially fibrous calcite occur in, and on the surface of, calcareous travertine being deposited from water of the Orenda Spring, Saratoga Springs, New York State. Field observations suggest that spheroids form by the precipitation of calcite on the surface of water droplets that contain newly formed bubbles of CO 2 . Although many of the spheroids subsequently disintegrate, some grow by the addition of laminae consisting of radial bundles of fibrous calcite, commonly separated by thin (? seasonal) laminae of fine-grained calcite and detritus. These spheroids are either incorporated into laminar travertine sheets or grow by successive increments into fresh-water ooliths and pisoliths with both a concentric and a radial structure.