Complex sentence: In 1903, McMartin established himself in Cornwall, Ontario, where he was president of the Labrador Pulp and Paper Company and of the Motherlode Sheep Creek Mining Company, and vice-president of Hollinger Consolidated Mines.
Split into simpler sentences: In 1903, McMartin established himself in business in Cornwall, Ontario. He was president of the Labrador Pulp and Paper Company and of the Motherlode Sheep Creek Mining Company and vice-president of Hollinger Consolidated Mines.