sandstones, shales and marls.Molding - process of manufacturing by shaping pliable raw material using a rigid frame or model called a mold.Monocline - A fold with a single limb which produces a sudden steepening of the dip; the rocks however soon approximate to horizontal on either side of this flexure.Monoclinic (crystal) - Three crystal axes are of unequal lengths and one intersection oblique (other two perpendicular)Moraine - glacially formed accumulation of unconsolidated debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age.Mullion (geology) - a particular type of reworked boudin (term likely derived from an architectural structure with the same name).Muscovite - The common or white mica; for the most part an orthosilicate of aluminium and potassium, crystallising in the monoclinic system.N[edit]Namibian age - 900 to 542 Ma (Neoproterozoic)Neogene - a geologic period starting 23 million years ago and lasting either until today or ending 2.6 million years ago with the beginning of the Quaternary.Non-clastic - Chemically/organically deposited rocks. Limestones, chalks, evaporite deposits gypsum.Normal fault - Dip-slip faults can be sub-classified into the types "reverse" and "normal". A normal fault occurs when the crust is extended. Alternatively such a fault can be called an extensional fault. The hanging wall moves downward, relative to the footwall.O[edit]Oligoclase - One of the plagioclase feldspars consisting of the albite and anorthite molecules combined in the proportions 9:1 to 7:3. It is found especially in the more acid igneous rocks.Olivine - Orthosilicate of iron and magnesium, crystallising in the orthorhombic system which occur widely in the basic and ultramafic igneous rocks, and includes olivine-gabbro, olivine dolerite, olivine-basalt, peridotites etc.Ordovician - The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 485.4 1.9 to 443.4 1.5 million years ago. It follows the Cambrian Period and is followed by the Silurian Period.Orogenesis - the formation and growth of mountains related to tectonic activity.Orogeny - refers to forces and events leading to a large structural deformation of the Earth's lithosphere (crust and uppermost mantle) due to the engagement of tectonic plates and is the primary mechanism by which mountains are built on continents.Orthoclase Silicate of potassium and aluminium. Monoclinic crystal form. Occurs as essential constituent in granitic and syenitic rocks and as accessory in many other rock types.Orthogeosyncline - A geosyncline between continental and oceanic cratons containing both volcanic and non-volcanic belts.Orthorhombic - Crystal structure with three perpendicular axes all of different lengths.Orthosilicate - Obsolete classification based on salt of hypothetical orthosilicic acid. Cf MetasilicateOxbow lake - a crescent-shaped lake found within a floodplain or fluvial terrace created by the cut-off and abandoned of an active meander loop by the meandering of a river.P[edit]Pahoehoe lava - Vesicular, basaltic lava often with ropy surface texture.Paleocurrent - An indication of the direction of fluid flow (at the time of deposition) found in a rock.Palaeozoic - the earliest of three geologic eras of the Phanerozoic Eon, spanning from roughly 541 to 252.2 million years ago. It is the longest of