<P> L (Limnic) horizons or layers indicate mineral or organic material that has been deposited in water by precipitation or through the actions of aquatic organisms . Included are coprogenous earth (sedimentary peat), diatomaceous earth, and marl; and is usually found as a remnant of past bodies of standing water . </P> <P> In addition to the main descriptors above, several modifiers exist to add necessary detail to each horizon . Firstly, each major horizon may be divided into sub-horizons by the addition of a numerical subscript, based on minor shifts in colour or texture with increasing depth (e.g., B21, B22, B23 etc .). While this can add necessary depth to a field description, workers should bear in mind that excessive division of a soil profile into narrow sub-horizons should be avoided . Walking as little as ten metres in any direction and digging another hole can often reveal a very different profile in regards to the depth and thickness of each horizon . Over-precise description can be a waste of time, and as a rule of thumb, layers thinner than 5 cm (2 inches) or so are best described as pans or segregations within a horizon rather than as a distinct layer . </P> <P> Suffixes describing particular physical features of a horizon may also be added . These vary considerably between countries, but a limited selection of common ones are listed here: </P> <Ul> <Li> b: buried horizon . </Li> <Li> c: presence of mineral concretions or nodules, perhaps of iron, aluminium, or manganese . </Li> <Li> d: root restricting layer . </Li> <Li> f: frozen soil (permafrost). </Li> <Li> g: a gleyed horizon . </Li> <Li> h: accumulation of organic matter . </Li> <Li> p: disturbed by ploughing or other tillage practices (A horizon only). </Li> <Li> r: weathered, digable bedrock . </Li> <Li> s: sesquioxide accumulation . </Li> <Li> w: weak development . </Li> <Li> x: fragipan . </Li> </Ul>

Describe the contents of the three soil horizons