https://www.usgs.gov/publications/stratigraphic-framework-and-depositional-sequences-lower-silurian-regional-oil-and-gas
This chapter is a re-release of U.S. Geological Survey Scientific Investigations Map 2916, of the same title, by Ryder (2006).
in thelower silurianstratigraphicframeworkdepositional
https://www.nist.gov/stonewall/description/lower-silurian?page=0%2C3
lower silurian