Editing DF2014:Stone layers

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[[File:stone_layers_prev.jpg|thumb|301px|right|A cliff walls with stone layers.]]There are four types of '''stone layers''' in ''Dwarf Fortress'', very much based on real-life geology ([[#In real life|see below]]). [[Stone]] layers are roughly homogeneous layers of rock, composed of the same kind of stone, that usually contain different ores. Each stone layer has its distinct markers and qualities; sometimes a clear dividing line can be drawn between two [[biome]]s from the stone layers underneath, sometimes not. Digging deeper, or into another local biome, will reveal differences between the layers' contents and a progression from sedimentary down to igneous.

These changes are usually quite sharp; fifteen layers may be mostly [[quartzite]], but the next thirty may be dominated by [[gabbro]]. Three-dimensional variance is planned for the future, but for now, changes between stone layers also mark changes in [[ore]] and [[gem]] content.

== Soil ==
{{main|Soil}}
Most maps have one layer of [[soil]] at the very top, although this layer may actually run the gamut from completely non-existent to ten or more layers deep. Note that on mountainous terrain soil tends to accumulate near edges; thus you can have partial soil "layers" down the side of the mountain for quite a few z-levels.

Soil is important for three reasons: it is easily [[farming|farmed]] (not requiring [[irrigation]] like stone does), it is easily [[miner|mined]] (taking less time than stone), and it does not leave any loose [[stone]] behind when mined. Soil layers can contain [[clay]] and [[sand]], if your biome has any, as well as a high chance of being an [[aquifer]], if your biome has one. Soil layers do not contain ores or gems, and '''at least one layer of soil''' is necessary to easily establish farming. It's ''not'' recommended you establish your main fortress in soil, as it cannot be [[smoothing|smoothed]] or [[engraving|engraved]] to make it visually appealing/more valuable.

== Sedimentary ==
{{main|Sedimentary layer}}
The [[sedimentary layer]] has an 80% chance of being the first stone layer that appears after any soil. It will include any [[lignite]] or [[bituminous coal]], if you are lucky enough to have some. [[Iron]] [[ore]] and all but one of the [[flux]]es is common here as well, making the sedimentary layer make-or-break for [[steel]] production. Note that this layer and the igneous extrusive are mutually exclusive, and will never be found in one place. Sedimentary layers are generally where the bulwark of the fortress will find itself, will contain most of the ores marked on the [[embark]] screen as "shallow metals", and is a good choice for [[exploratory mining]].

Note, however, that it is poor in [[gem]] content - those found in sedimentary layers are generally less valuable than those further down. Some types of sedimentary rock may contain an aquifer.

Common stone types: [[sandstone]], [[limestone]], [[shale]]

== Igneous extrusive ==
{{main|Igneous extrusive layer}}

In certain regions, igneous extrusive layers replace the sedimentary layers, but when present are not limited to the top-most layers and can appear anywhere except the bottom-most layer. Although being made of different rocks, they are similar to sedimentary layers, with the exception being that they often indicate the presence of [[magma]] above the [[magma sea]] itself. This is always the topmost layer near [[volcano]]es; the biggest stumbling block is that its presence means that the biome rarely contains any flux.

Common stone types: [[basalt]], [[rhyolite]]

== Metamorphic ==
{{main|Metamorphic layer}}

Can appear at any level except the bottom-most layer or above any sedimentary layer. Contains a small variety of [[vein]] ores, moderately valuable gems, and possibly can be [[marble]], the one non-sedimentary flux stone. It does lack weapon-quality [[ore]]s (containing only [[copper]] and [[silver]]).

Common stone types: [[schist]], [[gneiss]]

== Igneous intrusive ==
{{main|Igneous intrusive layer}}

Igneous intrusive layers can appear at any level except the top-most or above any sedimentary, and the deepest and often the thickest layer will always be igneous intrusive, just above the [[magma]] sea or [[semi-molten rock]]. Gems here are generally the most valuable, on average, with the most valuable of them all, colored diamonds, found in [[kimberlite]] in [[gabbro]] layers.

Common stone types: [[granite]], [[gabbro]]

== In real life ==

Being modelled on basic geology, much of the way stone layers work in ''Dwarf Fortress'' also applies to our planet: At the surface of the world there's a thin covering of [[soil]], a soft mixture of minerals (the building blocks of stones), small rocks ([[sand]], [[silt]], [[clay]] etc.), liquids, living things and so on.  Below that there's a [[sedimentary layer]] of stones; these are made of particles of minerals, organic detritus and other stuff, which, after tumbling around, end up settling down below ("sedimenting").  Those grains and particles are then glued together into new rocks ("cemented") by various processes; for example, by mineral growth of substances carried by water (similar to how stalactites grow).

Below the sedimentary layer, the rocks are subjected to heat from below, and pressure, stretching etc. from the movement of continental plates.  Those forces transform them into different kinds of rocks, called [[Metamorphic layer|metamorphic]].                                                         

Further down, as things get hotter still, rocks melt into [[magma]].  If magma escapes the heat, it may cool and harden while still underground, forming the [[igneous intrusive]] ("fiery [[inside]]") rocks.  In DF, these form a layer below the metamorphic stones, but in real life they may form anywhere there are cracks for the magma to fill in.  If the magma rises all the way up to the surface and is expelled by a [[volcano]], we call it lava.  The lava cools down into [[igneous extrusive]] ("fiery [[outside]]") layers, which in DF replace the sedimentary layers in some [[biome|biomes]] near volcanoes.

{{Category|Stone Layers|*}}
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