The heavy mineral suite of the St. Peter sandstone is rather uniform over large areas, but there is a pronounced concentration of leucoxene and ilmenite in south-central Wisconsin. Zircon, tourmaline, leucoxene, and ilmenite compose about 97 per cent of the heavy minerals, with anatase, ceylonite, apatite, rutile, staurolite, and garnet constituting the other 3 per cent. Pyrite, celestite, jarosite, and dahllite are present in minor quantities, but in some cases they flood the sample. The heavy mineral inclusions within the quartz grains were recovered by means of a new procedure and were found to be different from those associated with the quartz grains and to consist of zircon, apatite, biotite, hornblende, titanite, rutile, ilmenite, garnet, pyrite, tourmaline, fluorite, kyanite, and leucoxene. The quartz grains, classified on the basis of inclusions as suggested by Mackie, indicate that the ultimate source of the sands of the St. Peter was largely a granitic terrane. The immediate source seems to have been a sedimentary terrane.