But whole statues and pictures engraved on rocks and walls of granite and freestone, are inconvenient registers. Hence one well known form was soon allowed to stand as the sign of a subject or action; part of that figure might, in time, be substituted for the whole. The forms of animals whose qualities were supposed to bear relation to those of man, were admitted to represent abstract ideas; as, for instance, in India, the elephant’s head adorned the shoulders of the god of wisdom, and in Egypt, the watchfulness of the cat procured her the honour of lending a mask sometimes to the greatest of the goddesses. Insects whose appearance was constant at particular seasons, became the types of those seasons, or of the heavenly bodies which regulate them; so by a natural process, a scheme of hieroglyphic representation, if we must not say writing, was framed, which long continued in use among the governing priests of Egypt to preserve the annals of the country. Their hieroglyphics were themselves too cumbrous for constant use, and it appears certain from ancient tradition and modern discovery, that they produced a variety of steps approaching more or less to alphabetical writing; and in all probability the learned priests who could not be ignorant of the existence of such writing, preferred their own mysterious and obscure characters for the sake of that power which unusual and exclusive knowledge always confers. The effect that the use of hieroglyphic painting, whether more or less near to writing, had upon the art of painting itself was most disastrous. Those who were permitted to paint at all, were bound to make no improvement. The art was jealously kept for the adornment of hideous mummy cases[29] and sepulchral chambers, where the nearest approaches to what is properly painting were a sort of portraits, drawn upon the inner coffins, which were composed of folds of linen prepared with a chalk ground, or basso-relievos either coloured themselves, or imitated in flat colours upon the walls. The wood upon which the commoner coffin-painting was executed appears to have been sycamore; it was prepared with fine lime, mixed with some kind of gum or size for the colourer. The pigments were ochres for the most part; but the blues and greens appear to have been prepared from copper. The black was lamp-black, and the white a very fine lime[30]. These colours when applied on wood, or cotton, or linen, were probably mixed with gums, probably gum arabic or the Sarcocolla, which the Egyptians used in preparing their mummies, and also for glue[31], and that gum probably formed part of the varnish found on the mummy cases. According to Mr. Wilkinson’s account, the pictures in the catacombs were executed either on the bare limestone wall, or on the sandstone prepared with fine lime. Whether the groups were to be painted or chiselled in intaglio or relief, they were outlined with red ochre, then corrected with black.