Vertical accretion of fluvial conglomerate and sandstone units is common in tectonically active and rapidly subsiding basins. In such basins it is common to find coal or wind blown tuff interlayered with coarse conglomeratic deposits. Simple vertical sequences of grain size and sedimentary structures are difficult to establish. Upward-coarsening and upward-fining cycles coexist. The most characteristic features of these progradational fluvial successions are sole marks similar to flute casts which seem to have formed when pulses of coarse material scoured into finer deposits of lowland swamps. Examples of this type of environment are known in the Eocene and Oligocene of the northwestern Canadian Cordillera. Recent examples should be expected in areas where swampy lowlands are close to tectonically active mountain fronts and where alluvial fans cannot develop due to rapid subsidence.