During Early and Middle Devonian time, carbonate successions were deposited on the Mackenzie Platform in the east, on the Yukon Stable Block in the west, and on two small isolated platforms: the White Mountains Platform in the north and the Royal Mountain Platform in the south. During the same time interval, successions consisting largely of shale were deposited in the central Richardson Trough and in the peripheral Blackstone, Selwyn, Hazen and Rapid troughs. The Lower and Middle Devonian successions on the Mackenzie Platform consist of the Unnamed carbonate unit, along with the Cranswick, Hume, and Hare Indian formations. Slope deposits comprising a tongue of the Road River Formation and the Mount Baird Formation are transitional between the Mackenzie Platform and Richardson Trough. On the Yukon Stable Block in the west, the carbonate succession consists of the Kutchin and Ogilvie formations and an Unnamed shale unit. A succession showing a fluctuation between basinal shale and carbonate platform deposits comprises the Road River and Michelle formations in the Blackstone Trough, and the Ogilvie Formation and the Unnamed shale unit on the Yukon Stable Block. During the same interval, deeper water sediments of the Road River Formation were deposited in the troughs. The uppermost Middle and Upper Devonian successions are completely different from older Devonian sedimentary rocks, comprising the Canol, Imperial and Tuttle formations. The upper Middle Devonian Canol Formation is a widespread dark euxinic shale which is locally separated from underlying rock units by an unconformity. The succeeding Upper Devonian Imperial and Tuttle formations consist of fine to coarse grained clastic rocks of turbidite origin derived from an uplifted area in the north. The Tuttle Formation capping the succession is dated by spores as latest Late Devonian and Early Carboniferous.