A study was made of the dispersion of fundamental Rayleigh-mode surface waves along a line in the Superior Province of the Canadian Shield, from Flin Flon, Manitoba to Thunder Bay, Ontario, (a distance of 1121 km). The two-station method together with multiple filter analysis was used to determine the interstation group velocities of surface waves from five Alaskan earthquakes. The observed dispersion was then inverted to obtain the average shear velocity as a function of depth. The data are found to indicate a typical shield velocity structure and a crustal thickness of 40 ± 3 km. The results agree well with body-wave seismic studies conducted in the same area, and when these observations are combined with the results of this study, they yield an interestingly high Poisson's ratio (0.275 ± 0.007) for the lower crust.