Following seismic observations in the Albertan plains from the Ripple Rock explosion, a refraction line some 81 mi. long and parallel to the frontal thrust of the Rocky Mountains and about 60 mi. to the E. thereof was observed by 2-way shooting. Fifteen seismic parties, spaced at roughly uniform intervals along the line and using the method of close geophone correlation, were employed, the object being to map as many refractors or reflectors as possible as far as the Mohorovicic discontinuity. The results indicate that this discontinuity occurs at a minimum depth of 43 km. where the velocity is about 8.2 km./sec., while an intermediate layer with a minimum depth of 29 km. and velocity 7.2 km./sec. has been registered. Other intermediate refractors were observed. These results are compared with those obtaining in other parts of the American continent and elsewhere. The operational, instrumental, and theoretical aspects of the work are discussed.