Vincent Grafhorst / Minden / River in sandstone cave, Sof Omar Cave, Ethiopia

Jack Dykinga / Eroded Chinle shale mounds with colour bands, beneath the Paria Plateau, Vermilion Cliffs National Monument, Paria Canyon Vermilion, Arizona, USA.

Jouan Rius / Sandstone formations in Goblin Valley State Park, Utah, USA November 2012

Jouan Rius / Sandstone cliff at sunset, Colorado Plateau, Kodachrome Basin State Park, Utah, USA November 2012

Jouan Rius / Sandstone monoliths, Colorado Plateau, Kodachrome Basin State Park, Utah, USA November 2012

Juan Carlos Munoz / Rocks / pebbles and Flysch - a sequence of sedimentary rocks. Sakoneta beach, Deva, Gipuzkoa, The Bay of Biscay, Spain, June.

Juan Carlos Munoz / Flysch - a sequence of sedimentary rocks. Sakoneta beach, Deva, Gipuzkoa, The Bay of Biscay, Spain, June.

Orsolya Haarberg / Coastal sedimentary rocks (sandstone, mudstone, dolomite, limestone) Vardo, Finnmark, Norway, July 2006.

Orsolya Haarberg / Layers of different coloured sedimentary rocks (sandstone, mudstone, dolomite, limestone) Vardo, Finnmark, Norway, July 2006.

Visuals Unlimited / The red layers are paleosols or ancient soils in the Eocene John Day Formation, John Day National Monument, Oregon, USA.

Albert Lleal / Diatom (Amphora sp) SEM close-up view of fossil at 3500x magnification, approximately 2000 years old, found in lake near Huesca, Spain

Albert Lleal / Holothuroidean (Oneirophantites tarraconensis) fossil, 15 cm in length, Spain

Jeff Foott / Sandstone rock formations with hiker, Vermilion Cliffs National Monument, Colorado Plateau, Utah

Yva Momatiuk & John Eastcott / Skyline Arch sandstone formation, Arches National Park, Utah

Yva Momatiuk & John Eastcott / Sandstone rock formations, Coyote Buttes, Paria Canyon, Arizona, 360 view

Yva Momatiuk & John Eastcott / Hoodoo rock formations at sunrise, Bryce Canyon National Park, Utah

Yva Momatiuk & John Eastcott / Colorado River at Horseshoe Bend, Colorado River, Glen Canyon National Recreation Area, Arizona

Jeff Foott / Full moon over Balanced Rock formation, Arches National Park, Utah

Jeff Foott / Mule-ears (Wyethia amplexicaulis) flowers at the The Organ, Arches National Park, Utah

Jeff Foott / Marching Men sandstone formation, Arches National Park, Utah

Jeff Foott / Winding road and sandstone formations, La Sal Mountains, Arches National Park, Utah

Jeff Foott / Sandstone rock formations, La Sal Mountains, Arches National Park, Utah

Jeff Foott / Sandstone rock formations, Theodore Roosevelt National Park, North Dakota

Chien Lee / Limestone rock formations, Snow Mountains, Papua, Indonesia

Chien Lee / Limestone pinnacles, Tsingy de Bemaraha National Park, Madagascar

Vincent Grafhorst / River in sandstone cave, Sof Omar Cave, Ethiopia

Jeff Foott / The Citadel Ruins, Cedar Mesa area, Bears Ears National Monument, Utah

Tim Fitzharris / The Windows Section from Double Arch at sunrise, Arches National Park, Utah

Tim Fitzharris / The Windows Section from Double Arch at sunrise, Arches National Park, Utah

Yva Momatiuk & John Eastcott / Sandstone rock formations, Vermillion Cliffs National Monument, Arizona

Ingo Arndt / Milky way over sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota

Colin Monteath/ Hedgehog House / Wildflowers and sandstone rock formation, Flinders Ranges, South Australia, Australia

Albert Lleal / Trilobite fossils, Spain

Albert Lleal / Mollusc shell fossil, Tarragona, Spain

Albert Lleal / Trilobite fossil, Spain

Yva Momatiuk & John Eastcott / Petrified wood log with intricate patterns and colors, Petrified Forest National Park, Arizona

Yva Momatiuk & John Eastcott / Small sandstone canyon carved by water, exposes strong pattern of parallel lines, Vermilion Cliffs National Monument, Colorado Plateau, Utah

Yva Momatiuk & John Eastcott / Colorful sandstone patterns of lines, ridges and ripples, carved by erosion, are reflected in rainwater pool, Vermilion Cliffs National Monument, Colorado Plateau, Utah

Yva Momatiuk & John Eastcott / Toadstool Caprocks created by erosion, near Paria River, Grand Staircase-Escalante National Monument, Utah

Yva Momatiuk & John Eastcott / Cirrus and cumulus clouds over mesa, Monument Valley Navajo Tribal Park, Arizona

Pete Oxford / Stone forest of eroded limestone pinnacles, Yunnan Province, China

Pete Oxford / Fossil of Ammonite, Madagascar

Gerry Ellis / Hoodoo formations from Sunrise Point, Bryce Canyon National Park, Utah

Tim Fitzharris / Storm clouds over the Colorado River at Horseshoe Bend near Page, Arizona