The origin of the black colour is also question of doubt. It is generally ascribed to the presence of organic matter, but this material is scarcely present in sufficient quantity to account for the blackness altogether and it is quite possible that some of the colour at any rate is due to mineral matter. Chemically, black cotton soil shows no very striking differences from other Indian soils. The proportions of iron, alumina, lime and magnesium are fairly high, particularly the latter; while of the more essential plant foods, oaths appears to be present relatively in more abundant quantity than phosphorous and nitrogen. If compared with English soils the amounts of phosphates and nitrogen do certainly appear to be  small and this fact has doubtless given currency to the idea that the black cotton soil is becoming impoverished. With the exception, however, of certain alluvial deposits in Assam this soil compares favorably with the generality of Indian soil in this respect. Physically regar is essentially a clay soil and as such is very sticky when wet, retentive of moisture and easily loses its tilth if cultivated at the wrong time. The presence of lime,  however, to a certain extent counteracts these qualities and renders the soil friable when dry besides giving it its host characteristic property, that of shrinking and cracking, This property is due to flocculation of the clay particles in the presence of a dilute solution of some lime compound, but the contraction thereby caused only become apparent when the soil dries. The best regar land contains very few large particles, but inferior qualities frequently contain nodular limestone or kankar. This deposition of a calcareous pan is of general occurrence in soils of arid regions. In the east of District the underlying rock is crystalline and yields a soil more sandy and pervious than regar and one therefore more adaptable to irrigation. Where the two geological formations intermix a free working loam is obtained, but this is not found over any large area.