With the exception of the River Tone, which appears to have been separated at an early stage from its neighbours to the south by
a major fault, the rivers of south Somerset and east Devon were initiated on a southward dipping Tertiary planation surface.
The evolutionary histories of the present-day catchments of the rivers Exe and Otter are complex and inter-related. Those of the
adjacent Axe and Teign appear to be less complex and may have evolved relatively independently from the Exe-Otter system.
The differences in the histories of the catchments are most clearly demonstrated by their terrace systems. The Exe-Otter
catchment has 10 or more terrace levels at heights of up to 140 m above the modern floodplain. In contrast, the Axe, Teign and
Tone catchments contain only one or two terrace levels all of which are less than 20 m above the present-day valley floor.
The explanation suggested here for the difference involves a sequence of river captures that changed the forerunner of the
present-day Otter from a major river capable of producing a 3-km wide gravelly braidplain into a minor stream
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