Japanese words equivalent to the terms Palaeogene and Neogene

The geochronologic units of Palaeogene and Neogene have long been described in Japanese as "Kodaisanki" and "Shindaisanki", which mean old and young Tertiary, respectively. The International Commission on Stratigraphy, however, recently proposes the revised geochronologic chart, demonstrating the subdivision of the Cenozoic Era into the Palaeogene and Neogene Periods instead of the Tertiary and Quaternary. The Japanese wording "Kodaisanki" and "Shindaisanki", therefore, should be reconsidered in terms of derivatio nominis of Palaeogene and Neogene. Here we review the Japanese usages of Palaeogene and Neogene in previous textbooks back to the end of the nineteenth century. It is concluded that the words "Koseiki", "Shiseiki" or "Kyuseiki" for Palaeogene and "Shinseiki" or "Kinseiki" for Neogene have already been proposed and described by Prof. Matajiro Yokoyama. These Japanese terms for Palaeogene and Neogene would be taken into consideration to write geological reports and papers in Japanese.