it completely with a facing of burnt brick, which sometimes extends to as much as ten feet in thickness.  The burnt brick was thus made to protect the unburnt from the influence of the weather, while labor and fuel—­were greatly economized by the employment to so large an extent of the natural substance.  The size and color of the bricks vary.  The general shape is square, or nearly so, while the thickness is, to modern ideas, disproportionately small; it is not, however, so small as in the bricks of the Romans.  The earliest of the baked bricks hitherto discovered in Chaldaea are 11 1/4 inches square, and 2 1/2 inches thick, while the Roman are often 15 inches square, and only an inch and a quarter thick.  The baked bricks of later date are of larger size than the earlier; they are commonly about 13 inches square, with a thickness of three inches.  The best quality of baked brick is of a yellowish-white tint, and very much resembles our Stourbridge or fire brick; another kind, extremely hard, but brittle, is of a blackish blue; a third, the coarsest of all, is slack-dried, and of a pale red.  The earliest baked bricks are of this last color.  The sun-dried bricks have even more variety of size than the baked ones.  They are sometimes as large as 16 inches square and seven inches thick, sometimes as small as six inches square by two thick.  Occasionally, though not very often, bricks are found differing altogether in shape from those above described, being formed for special purposes.  Of this kind are the triangular bricks used at the corners of walls, intended to give greater regularity to the angles than would otherwise be attained; and the wedge-shaped bricks, formed to be employed in arches, which were known and used by this primitive people.

The modes of applying these materials to building purposes were various.  Sometimes the crude and the burnt brick were used in alternate layers, each layer being several feet in thickness; more commonly the crude brick was used (as already noticed) for the internal parts of the building, and a facing of burnt brick protected the whole from the weather.  Occasionally the mass of an edifice was composed entirely of crude brick; but in such cases special precautions had to be taken to secure the stability of this comparatively frail material.  In the first place, at intervals of four or five feet, a thick layer of reed matting was interposed along the whole extent of the building, which appears to have been intended to protect the earthy mass from disintegration, by its protection beyond the rest of the external surface.  The readers of Herodotus are familiar with this feature, which (according to him) occurred in the massive walls whereby Babylon was surrounded.  If this was really the case, we may conclude that those walls were not composed of burnt brick, as he imagined, but of the sun-dried material.  Reeds were never employed in buildings composed of burnt brick, being useless