A N. American stage (491–471.8 Ma ago) of the Palaeozoic era, preceded by the Sunwaptan and followed by the Whiterockian.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。