| A Archean |
| C Carboniferous |
| CD Carboniferous and Devonian |
| Cm Cambrian |
| CmPt Cambrian-Proterozoic |
| D Devonian (undivided) |
| DS Devonian and Silurian |
| Lakes and wide rivers |
| Arctic areas covered by Ice |
| J Jurassic (undivided) |
| JTr Jurassic and Triassic |
| K Cretaceous (undivided) |
| KJ Cretaceous and Jurassic |
| Mi Acidic Mesozoic intrusive rocks |
| N Neogene |
| NPg Neogene and Paleogene |
| O Ordovician |
| OCm Ordovician-Cambrian |
| P Permian |
| PC Permian-Carboniferous |
| Pz Paleozoic (undivided) |
| Pg Paleogene |
| PgK Paleogene and Cretaceous |
| Pi Paleozoic intrusive rocks |
| Pt Proterozoic |
| PtAi Acidic Proterozoic and Archean intrusive rocks |
| Q Quaternary (undivided) |
| QT Quaternary and Tertiary |
| Qv Extrusive rocks Pliocene and Quaternary |
| S Silurian |
| Sea and large lakes |
| SO Silurian-Ordovician |
| TKi Acidic intrusive rocks Cretaceous, Paleogene and Neogene |
| Tr Triassic |
| TrP Triassic and Permian |
| X Lower and Middle Proterozoic |
| Y Upper and Middle Proterozoic |
| Z Upper Proterozoic |
| ii Basic, Ultrabasic and Alkaline intrusive rocks of unknown age |
| Areas outside of the former Soviet Union |
| pC Precambrian (undivided) |
