The Lewis Hills massif is interpreted as having been formed at an oceanic fracture zone (FZ) prior to its obduction. The compositions of minerals in the residual mantle and cumulate rocks of the massif are similar to those in other massifs of the Bay of Islands ophiolite and those in comparable rocks from the oceanic basins. The residual mantle rocks consist of olivine (Fo89.9--91.7, NiO=0.37--0.46%), orthopyroxene (100*Mg/ ranges from 90.6 to 91.8), spinel (100*Cr/ =43.7--57.4 and 100*Mg/2+>=51.2--67.7), and rare clinopyroxene. These minerals have compositions similar to those of the most depleted abyssal peridotites. The cumulate units are mixtures of olivine (Fo88.8--78.0, NiO=0.32--0.08), plagioclase (An88.4--68.8), clinopyroxene (100*Mg/=93.0--75.6) and Cr-Al spinel (100*Cr/=36.0--8.8 and 100*Mg/2+>=73.7--50.0). The ultramafic cumulates appear to have crystallized at moderate to high pressures and the gabbroic rocks at low pressures. Differences between the magmatic processes recorded in the Lewis Hills massif during its formation adjacent to a FZ and those inferred for the North Arm Mountain massif while it formed more distantly from the FZ are (1) the more depleted nature of the mantle near the FZ (2) the higher TiO2 contents of diabase dikes near the FZ, (3) the greater abundance of feldspathic ultramafic rocks near the FZ, and (4) the absence of orthopyroxene as a cumulate phase near the FZ. ¿ American Geophysical Union 1988