[1] Frederic William Harmer (1835-1923) proposed the same causation and timing in 1907 having considered glacial lake sediments found on the Shropshire Plain.
The market town of Newport, Shropshire, sits atop a sandstone ridge, which in the last ice age was an island or peninsula in Lake Lapworth.
Long after the supposed lake had vanished, early man fished here, and two log boats were uncovered one mile (1.6 km) from Newport.
It is but one of several such buried trenches known beneath the surface of Shropshire and Cheshire whose form indicates erosion by sub-glacial meltwater under considerable pressure, the long profile of this and others being undulating, i.e. with water flowing uphill in certain sections.
It is postulated that this sub-glacial version of the Severn rose to the surface at the ice front and cut the gorge; no lake is required in this scenario.