In proportion as it contains the last, the kunkur is more or less red.
That which contains none is of a dirty-white.

It is found in many parts of India in thin layers, or amorphous masses, formed by compression, upon a stiff clay substratum; but in Oude I have seen it only in nodules, usually formed on nuclei of flint or other hard substances.

The kingdom of Oude must have once been the bed, or part of the bed, of a large lake, formed by the diluvial detritus of the hills of the Himmalaya chain, and, as limestone abounds in that chain, the bed contains abundance of lime, which is taken up by the water that percolates through it from the rivers and from the rains and floods above.

The lime thus taken up and held in solution with carbonic add gas, is deposited around the small fragments of flint or other hard substances which the waters find in their way.

Where the floods which cover the surface during the rains come in rivers, flowing from the Himmalaya or other hills abounding in limestone rocks, they of course contain lime and carbonic-acid gas, which add to the kunkur nodules formed in the bed below; but in Oude the rivers seldom overflow to any extent, and the kunkur is, I believe, formed chiefly from the lime already existing in the bed.
Doctor O'Shaughnessy, the most eminent chemist now in India, tells me that there are two marked varieties of kunkur in India--the red and the white; that the red differs from the white solely in containing a larger proportion of peroxide of iron; that the white consists of carbonate of lime, silica, alumina, and sometimes magnesia and protoxide of iron.