Shawinigan Falls, 20 miles north of the St. Lawrence River and approximately midway between Montreal and Quebec, is 4½ miles1 north of the boundary between the pre-Cambrian shield and the St. Lawrence lowlands. The falls, from which the town gets its name and which are the source of the waterpower developed there, are in the St. Maurice River, which empties in the St. Lawrence River at Trois Rivières. North of Shawinigan Falls, crystalline rocks of the pre-Cambrian shield crop out; whereas, to the south, the St. Lawrence lowland is underlain by nearly horizontal Paleozoic rocks, covered by extensive sand-plain that here borders the St. Lawrence River.
In 1933, during the course of field work on commercial granites, for the Quebec Bureau of Mines,2 the writer mapped an area about Shawinigan Falls. At that time it was realized that the exposures about the town afford data on the . . .