The origin of the buried bedrock canyon of the Hudson river is clearly related to the cause of the canyon in the continental shelf, which extends to great depths. Obviously the submarine canyon cannot have been carved by ice. In my interpretation the canyon of the Hudson River was formed by a mechanism of in situ disintegration along joints or faults, and some of the disintegration product was washed out by fast currents, as the land was raised above the sea. In the steep section of the continental shelf, drift formerly present in the channel was mostly eroded away by currents. Organic sediments accumulated in the estuary since these catastrophic events.
Similar mechanisms can account for features of other fjords, that otherwise seem enigmatic.