Excavations for the St Lawrence Seaway uncovered igneous rocks which are, however, no longer to be seen. The form of the intrusion is not known. The rocks are banded and consist of kaersutite phenocrysts, rare grains of serpentinized olivine and pyroxene, and a fine groundmass of titanomagnetite, kaersutite, clinopyroxene, a little red biotite, nepheline and possible feldspar. Some rocks contain ocelli of analcime and dolomite. Numerous rock analyses are available.