MRS. ELIZABETH SIMCOE, the wife of the governor of Upper Canada (Ontario) in the 1790s, was an heiress and a member of the English ruling class in the days of its greatest self-confidence and power. Despite her cultured and protected upbringing, she reacted to life in the new province with fascination, not repulsion. With an open mind, she explored the evidence of its strangeness: two rattlesnakes brought to her in a barrel for examination, or sugar made from the black walnut, which she thought sweeter than that of the maple. The gentle-folk leaders of the Glengarry Highlanders assembled to meet her in their "national dress." Suspicious as she was of the bourgeoisie, attuned after the manner of her age to the virtues of the primitive, the Indians represented for her even more forcibly than the Highlanders the life of immemorial custom. All was raw material for her letters and diaries. These survive, with her sketches and watercolours, as the record of an unflinchingly intelligent observer. Back in England, Mrs. Simcoe survived her husband by more than 40 years, alert to the end, and surrounded by her busy, deferential daughters. She never returned to Canada, but remained a close observer of its affairs -- a strange story, to her increasingly conservative eyes, of American- style progress and of democratic discontent and rebellion. Her most intimate friend was the aunt of Sir Francis Bond Head, the governor of the time of Mackenzie`s rebellion. After Elizabeth Simcoe`s death in 1850 one of her repressed daughters staged her own rebellion by marrying a servant. Elizabeth Posthuma Simcoe 1762-1850: A Biography (Dundurn, 276 pages, $16-95 paper), by Mary Beacock Fryer, is well researched and as readable as a novel. It will delight everyone concerned with English upper-class life in the age of the Prince Regent or with the troubled rise of pioneer Ontario.