The Middle Devonian Acadian orogeny affected the entire Appalachian orogen from Newfoundland to Alabama with varying intensities of deformation and metamorphism. Part of the erosional debris from this uplifted area of tectonism was shed westward into the adjacent Appalachian basin. The basin subsidence and filling varied along its length, but not in concert with the adjacent tectonism. In the Early Devonian, the basin was stable with very little subsidence. Beginning in the Middle Devonian and continuing throughout the Late Devonian, the eastern part of the basin (now Pennsylvania and central New York) underwent rapid subsidence, where the largest volume and coarsest sediments were deposited as the Catskill Delta. To the southwest, grain size and thickness progressively decrease to the thin sequence of black shales in eastern Tennessee and Kentucky. To the north (northern New York, eastern Ontario and southern Quebec), no real evidence exists that a Devonian basin developed—the sediment from the orogenic zone probably passed over the Laurentian shield to the Michigan basin and perhaps elsewhere. The Acadian orogeny did not impinge upon the basin and its contained sediments, in distinct contrast with the Taconian and Alleghanian orogenies, both of which directly affected the basin, albeit in different ways. Reported Devonian structures within the basin are insignificant (growth folds), questionable (radiometric dating of faults), or probably incorrect (folding and angular unconformity). Acadian structures that occur between the basin and the main tectonic belt include open, upright folds and steep faults; cooling of Taconian metamorphic terrane during the Devonian and Early Carboniferous is also indicated for these rocks.