The Lower Devonian Seboomook Formation and Matagamon Sandstone in the area about Grand Lake Matagamon, northern Maine, comprise a westerly prograded delta-submarine slope complex, consisting of interbedded silty mudstone, turbidite beds, pebbly mud-stone, and slump units. Two channels with fills of siltstone and fine-grained sandstone and cut into fine-grained slope sediments are described. The smaller channel is contiguous with finegrained, graded levee deposits similar in texture and composition to the material cut by the channels. The assemblage of channels, abundant slumps in the extra-channel deposits, and other structures suggest gravity-induced deposition in a lower slope to base-of-slope environment. The size of the channels, meandering profile of the larger channel, and the sedimentary structures and texture of the fills indicate deposition on a submarine fan or rise. The data also indicate that most finegrained sediment outside the channels was transported downslope by partially channelized turbidity currents and overbank flows, much as materials are being deposited on modern subsea fans and continental rises.