Definition of "underlying"

Old Yew, which graspest at the stones⁠That name the under-lying dead,⁠Thy fibres net the dreamless head,Thy roots are wrapt about the bones.

1850, [Alfred, Lord Tennyson], In Memoriam, London: Edward Moxon, […], canto II

During the track renewals, advantage was taken to redrain the area and the old spent ballast was removed down to the underlying rock, new ballast and drains being provided throughout.

1950 January, “Re-Signalling at Liverpool Lime Street Station”, in Railway Magazine, page 43

Sometimes, the underlying layers are exposed by erosion, revealing the story of the rocks like an open book.

2012, Chinle Miller, In Mesozoic Lands: The Mesozoic Geology of Arches and Canyonlands National Parks, Kindle edition

The underlying problem with transport policy is that there no coherent strategy. Ministers have tended to encourage greater use of motor vehicles through both transport and (particularly) planning policies, while simultaneously warning of the terrible consequences of unfettered growth of road use.

2020 December 2, Christian Wolmar, “Wales offers us a glimpse of an integrated transport policy”, in Rail, page 56