Peat beds sometimes contain pockets of a mass with a handsome brown colour and consisting of a mixture of humic acids and other organic substances which may be ranked with the humin bodies that are always formed when organic matter decomposes in presence of an insufficient supply of oxygen. These bodies are dark coloured, mostly deep brown, rich in carbon, and, to some extent, similar to brown coal or peat in chemical composition. Their high carbon content renders these substances very inert towards chemical reagents, and therefore particularly adapted for the preparation of painters’ colours. Genuine Vandyke brown, which is the handsomest brown known, is an earth rich in humin compounds; and Cassel brown also belongs to this group. (G) BLACK EARTH The colour of these earths is entirely due to carbon, and pure carbon, a certain form of which occurs native, is itself used as a pigment. Actually, there are only two minerals that require to be mentioned in this connection: black schist and graphite. _Black Schist_ In most cases this is a clay shale, so rich in carbon as to appear deep black. In commerce, this mineral is also erroneously called “black chalk”; but at present it is seldom used as a pigment or drawing-material, black chalks being produced far more cheaply than the expense of preparing the natural article. Grey clay shales are used for making grey earth pigments (stone grey, and mineral grey). _Graphite_ This mineral is found, in a very pure state, in many localities, celebrated deposits occurring in England, Siberia, Bohemia and Bavaria, whilst North American graphite has lately come into prominence. Graphite is a modification of pure carbon, and is met with in the form of hexagonal (rhombohedral) crystals, usually occurring as hexagonal plates with a lustrous, iron-black colour. It rubs off easily, and readily burns away, leaving a very small amount of ash, when subjected to a very high temperature in presence of air. The principal uses of graphite are as an anticorrosive paint for iron, and for making lead pencils. As already mentioned, the term “earth colours” has been considerably broadened of late. Whereas, formerly, it was restricted to colours prepared exclusively from minerals by a simple treatment, limited to crushing, levigation or calcination, it now includes the pigments obtainable from large by-products of certain chemical processes. This latter class is especially important as affording an opportunity of utilising products formerly considered worthless and whose removal often entailed heavy expense.