Normal-moveout-corrected and stacked sections of wide-angle reflection data collected in the Archean Slave province and Paleoproterozoic Wopmay orogen in northwestern Canada image the crust-mantle boundary as a subhorizontal discontinuity at about 32--36 km depth along a 450 km lateral extent, and, for the first time from such data, layering within the lithospheric mantle at depths between 75 and 90 km over a lateral distance of 750 km. These images correspond to Moho and mantle reflections observed on a co-located multichannel seismic (MCS) reflection profile. Structural features and/or the basalt-eclogite phase change, associated with subduction of oceanic and/or delaminated lower crust, are possible sources of the deep reflectivity. One mantle reflection group lies west of the MCS data and east of the Cordilleran deformation front. It could have similar sources or result from the Mesoproterozoic Racklan orogen or Meso-Neoproterozoic rifting of the ancient margin. ¿ 1999 American Geophysical Union