TY - BOOK ID - 134521346 TI - The Helderberg Group and the position of the Silurian-Devonian boundary in North America PY - 1964 PB - Washington United States Geological Survey, Department of the Interior DB - UniCat UR - https://www.unicat.be/uniCat?func=search&query=sysid:134521346 AB - ER -