Among naturally-occurring materials of value for the improvement of soils. may be numbered peat, swamp or black muck, river, pond, mussel and marsh muds and similar deposits from both fresh and salt water. Many of these possess a distinct manurial value and applied liberally can frequently be used to advantage in the upkeep of fertility. They are not, however, to be regarded as in the same class as "fertilizers"--materials furnishing notable and well marked percentages of available nitrogen, phosphoric acid and potash—but rather as amendments, furnishing, chiefly, semi-decomposed vegetable (organic) matter which subsequently increases the humus content of the soil, or carbonate of lime, as the case may be, with small percentages of nitrogen and mineral plant food matter for the physical and chemical improvement of the soil. As a supplier of humus-forming material and nitrogen (largely inert), peat and swamp muck find their chief function and value, while the several classes of "muds" are perhaps more particularly useful for their mineral content and their influence on the texture or tilth of the soil to which they may be applied.