4. Soils formed from volcanic ashes or from materials moved by the wind and deposited in low places or in hills or ridges. 5. Those formed chiefly from the decay of vegetable matter, (tule, peat, muck). =48. Qualities of Soils.=—In respect of quality, soils have been arbitrarily divided into many kinds. Some of the more important of these divisions are as follows: 1. _Sand._ Soils consisting almost exclusively of sand. 2. _Sandy Loams._ Soils containing some humus and clay but an excess of sand. 3. _Loams._ Soils inclining neither to sand nor clay and containing some considerable portions of vegetable mold, being very pulverulent and easily broken up into loose and porous masses. 4. _Clays._ Stiff soils in which the silicate of alumina and other fine mineral particles are present in large quantity. 5. _Marls._ Deposits containing an unusual proportion of carbonate of lime, with often some potash or phosphoric acid resulting from the remains of sea-animals and plants. 6. _Alkaline._ Soils containing carbonate and sulfate of soda, or an excess of these alkaline and other soluble mineral substances. 7. _Adobe._ A fine grained porous earth of peculiar properties hereinafter described. 8. _Vegetable._ Soils containing much vegetable débris in an advanced state of decomposition. When such matter predominates or exists in large proportion in a soil the term tule, peat or muck is applied to it. With the exception of numbers six, seven and eight these types of soil are so well-known as to require no further description for analytical purposes. The alkaline, adobe and vegetable soils on the contrary demand further study. =49. Alkaline Soils.=—The importance of a more extended notice of this class of soils for analytical purposes is emphasized by their large extent in the United States. Chiefly through the researches of Hilgard attention has been called to the true character of these soils which are found throughout a large part of the Western United States and which are known by the common name of alkali. The following description of the origin of these soils is compiled chiefly from Hilgard’s papers on this subject. Wherever the rain-fall is scanty, and especially where the rains do not come at any one time with sufficient force to thoroughly saturate the soil and carry down through the subsoil and off through the drainage waters the alkali contained therein, favorable conditions exist for the production of the alkaline soil mentioned above. The peculiar characteristic of this soil is the efflorescence which occurs upon its surface and which is due to the raising of soluble salts in the soil by the water rising through capillary attraction and evaporating from the surface, leaving the salts as an efflorescence. Soils which contain a large amount of alkali are usually very rich in mineral plant food, and if the excess of soluble salt could be removed, these lands under favorable conditions of moisture would produce large crops.