In the iron ore claim of Grustagsgruvan at Vattholma, 20 km N of Uppsala the author has discovered an occurrence of subglacial limestone. It hat been deposited in sheltered cavities on one of the glacially-sculptured outcrops of iron ore. These outcrops were formerly covered by esker gravel. The subglacial limestone has the shape of oval concretions and knobs. They are often arranged in orientated rows and are formed by fine-grained sand and carbonate in about the same proportions. Several of the outcrops of iron ore are coated with gravel grains fixed to the substratum by carbonate. The concretions are interpreted as formed by erosion of a primary and partly diagenetisized filling of find-grained sand in the cavities. The carbonate is derived from the Cambro-Silurian or Archaean limestone material in the esker.