Deep seismic sounding along a line from Flin Flon to Mafeking, Manitoba, revealed the Conrad and M-discontinuites. With a single shotpoint it was found possible to determine velocities, layer thicknesses, and structure using the interpretational possibilities of head waves. The Conrad discontinuity rises from 15.5+ or -1 km near Flin Flon to about 10 km near Mafeking, while the M-discontinuity rises from 34+ or -1 km to 31+ or -1 km. Depths and densities related to the seismic model do not totally explain the observed gravity curve; this is believed to be due to the presence of masses of anomalous density within the granitic layer.
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Hall et al. (1965) studied this question.