Thomson’s artistic path was not always straight. To consider his varied and energetic sketches in total invites us to trace certain trends in his oeuvre. Fire Swept Hills is an agitated and chaotically messy elegy to what was once a mature forest: Thomson’s reaction to the land after fire has swept through and ravaged it. Charred spindles of trees standing precariously like lifeless skeletons remind viewers constantly of fire and destruction. In the lower half, a tumble of paint crashes over rocks and more burnt trunks and branches like a wild cataract. Blood reds, blues, ash greys, and whites, all jumbled and mashed violently together, complete its statement of confusion and disorder. In Cranberry Marsh, meanwhile, the normal landscape conventions of his earlier work begin to fade, his hues become more vibrant, and his compositions, while still recognizable as subjects, become battlefields for layers of close-hued or clashing paint.

These “drawings in paint” have long been considered the core of Thomson’s work. Most of them were not done as studies for larger canvases but as complete works in themselves. He was satisfied with these small gems because he realized, as did his mentors J.E.H. MacDonald (1873–1932) and Lawren Harris (1885–1970), that they would not translate to a large canvas without losing the intimacy that characterizes them profoundly. Only a dozen or so, including The Jack Pine, 1916–17, and The West Wind, 1916–17, were ever realized as large canvases.

The Haystack paintings by Claude Monet (1840–1926) or the large cut-paper collages by Henri Matisse (1869–1954) serve similar ends to Thomson’s panels: they form an extensive suite of paintings with a constant theme. Consistent in style and with a palette of strikingly original colours, the sketches were created with a specific intent and executed in a short window of opportunity. At one point Thomson said he wanted to produce an oil sketch a day of Algonquin Park’s changing scenes, shifting with the weather and the seasons.