In this paper we give data for An and Sr in plagioclase to demonstrate the presence of numerous amphibolite xenoliths within parts of a basic igneous mass where, after initial reconnaissance mapping, none was suspected. The data also show that the concentration of Sr in plagioclase from the margin of some amphibolite xenoliths is appreciably higher than in plagioclase from either the cores of the xenoliths or the enclosing metagabbro even though the modes and An contents of the plagioclase are similar. An explanation is offered, which implies that some of the xenoliths were amphibolites rather than anhydrous equivalents prior to their enclosure in the basic magma.