Natural England - Geology glossary (L to O)
Geology glossary (L to O)
This page of the glossary covers L to O. You can navigate to the next section from the links at the bottom of this page.
| Lava Molten rock (magma) that comes to the Earth's surface through a volcano or fissure |
| Limestone A sedimentary rock composed primarily of calcium carbonate. Some 10% to 15% of all sedimentary rocks are limestones. |
| Loess Material transported and deposited by wind and consisting primarily of silt size particles. |
| Magma Molten (melted) rock that forms naturally within the Earth. Magma may be either a liquid or a fluid mixture of liquid, crystals, and dissolved gases. |
| Mantle The middle layer of the Earth, lying just below the crust and consisting of relatively dense rocks. The mantle is divided into two sections, the upper mantle and the lower mantle; the lower mantle has greater density than the upper mantle. See also core and crust. |
| Marble A coarse-grained, metamorphic rock derived from limestone or dolomite. |
| Mesozoic An Era of geological time, dating from about 248 to 65 million years ago (comprising the Triassic, Jurassic and Cretaceous Periods). |
| Metamorphic rock A rock that has undergone chemical or structural changes without melting. Heat, pressure, or a chemical reaction may cause such changes. |
| Metamorphism The process by which metamorphic rocks are formed as a consequence of increased heat and pressure. |
| Moraine A single, large mass of glacial till that accumulates, typically at the end of a glacier. |
| Mudstone A layered sedimentary rock composed of clay-sized particles. |
| Nautiloid Nautiloids were primitive, thick-shelled, carnivorous marine invertebrates, related to the modern-day squid and octopus. They evolved during the Ordovician and are still around today, but are uncommon (only a single species, Nautilus, survives). They were most abundant during the Palaeozoic Era, roughly 400 million years ago. |
| Neogene The name given to the Period of geological time from 24 to 1.8 million years ago. |
| Old Red Sandstone Describes the terrestrial sedimentary and igneous rocks approximately equivalent in age to the Devonian marine rocks found in southwest England and Europe. |
| Oolite A limestone consisting largely of spherical grains of calcium carbonate. Each grain is made up of concentric layers of calcium carbonate and are known as ooliths. |
| Ordovician A Period of geological time, dating from about 495 to 443 million years ago. |
| Orogeny An episode of mountain building. |
| Outcrop A surface exposure of a particular unit of rock or sediment. |
| Outlier An area or group of rocks that are surrounded by rocks of an older age |
| Outwash Sediment, consisting of sand and gravel, that is deposited by meltwater in front of a glacier. |
