The same streaky argillaceous sandstones prevailed as in Karague.
"The Discovery of the Source of the Nile" by John Hanning Speke
The cliffs at Foul Point and Point Cunningham unite the sandstone and argillaceous formation.
"Discoveries in Australia, Volume 1." by J Lort Stokes
As a whole the formation is a large body of red calcareous and argillaceous sandstone and shale.
"History and Comprehensive Description of Loudoun County, Virginia" by James W. Head
The material of the hill, however, is not the hard argillaceous sandstone of the lock site, but merely alluvial.
"The Panama Canal and its Makers" by Vaughan Cornish