Related by context. Frequent words. (Click for all words.) 77 geological formations 63 rock formations 62 geologic formation 59 shale formations 58 geologically 56 shales 56 geologic 55 coal seams 55 caverns 55 sedimentary rock 54 salt domes 53 shale deposits 53 sedimentary basins 53 underground caverns 52 methane hydrate 52 subsurface 51 geological 51 permafrost 50 aquifers 50 basins 50 geology 50 methane hydrates 49 marine sediments 49 magma chamber 49 sandstones 49 sedimentary rocks 49 shale 48 landforms 48 rock outcrops 48 carbonate rocks 48 Lower Cretaceous 48 sedimentary basin 48 fossils 48 sediments 47 Eocene 47 Bakken formation 47 landform 46 lava tube 46 coal seam 46 Geologically 46 salt caverns 46 Bakken Formation 46 soils 46 Bakken shale 46 Carboniferous 46 cavern 46 reservoirs 46 peridotite 46 overlie 46 basalt 46 basalts 46 gas hydrates 46 sandstone 46 peat bogs 45 earth crust 45 drainage basins 45 glacial till 45 streambeds 45 Ogallala Aquifer 45 Sediments 45 lavas 45 limestone 45 lignite coal 45 shallow depths 45 Pliocene 45 astronomical objects 45 paleontological 45 tundra 45 St. Lawrence Lowlands 45 Ordovician 45 Miocene 45 hydrothermal 45 outcroppings 44 limestones 44 Paleozoic 44 zeolites 44 Marcellus wells 44 continental crust 44 abiotic 44 methane 44 injection wells 44 Late Cretaceous 44 reservoir 44 Marcellus Shale formation 44 alpine lakes 44 liquid hydrocarbons 44 Quaternary 44 skarn mineralization 44 aquifer 44 lithology 44 oceanic crust 44 Gippsland Basin 44 Earth crust 44 lava flows 44 coalbed methane 44 volcanic rock 44 Book Cliffs 44 marine reptiles 43 olivine 43 Appalachian basin 43 coalbed methane CBM