|Macro-fossil||Macrofossils are preserved organic remains large enough to be visible without a microscope. Plant macrofossils include leaf, needle, cone and stem debris; and can be used to identify types of plants formerly growing in the area. Algal macrofossils (eg brown kelp) are used to analyze prehistoric marine and aquatic ecosystems. Animal macrofossils include the teeth, skulls, and bones of vertebrates, as well as such invertebrate remains as shells.|
|Macrophyte||A large water plant|
|Magma||Molten (very hot, liquid) rock formed below the Earth's crust. It 'freezes' below 800–1000 °C|
|Mass movement||The downslope movement of the regolith (unconsolidated mud, stones, rocks) under gravity, caused by a number of different processes – saturation, freeze–thaw, etc|
|Metamorphic||Of rocks, formed from alteration of original rocks by heat, pressure or other processes in the Earth's crust|
|Metamorphism||The process by which rocks are altered by heat and pressure during mountain–building periods|
|Milankovich theory||The theory that the cyclical nature of ages Ice Ages is related to astronomical cycles – equinoxes, eclipses and oscillations – in the Earth's orbit over time. Named after Milutin Milankovich, a Yugoslav geophysicist working in the 1920s. Recently, increased support for the 'Milankovich theory' has recently come from several sources|
|Mixed woodland||Woodland containing both coniferous and broadleaved tree species|
|MLURI||Macaulay Land Use Research Institute. Based in Aberdeen, MLURI is the government agency and advisor responsible for the Soil Survey and Land Capability Survey and associated research in Scotland|
|Montane heath||A habitat found on the soils of high mountain summits, ridges and plateaux above the natural tree line. Consists of dwarf-shrubs, mosses and hardy grasses.|
|Muirburn||Seasonal burning of small strips and patches of heather moorland as a means of habitat management for red grouse. Encourages a mosaic of tall heather in which red grouse can take shelter, and new growth on which to feed|
|Munros||Mountains in Scotland at least 3000 ft (914 m) high. A list of such mountains was first published by Sir Hugh Munro in his Tables of Heights over 3000 feet in 1891. Today, these mountains are popularly walked (Munro–bagging) as a challenge, and the list is regularly reviewed|
A symbol for millibar - a unit of pressure.
Meltwater is created by melting snow and ice and it often picks up and carries deposits along with it.