Chaldaea was the cradle of the civilization, and consequently of the art, whose characteristics we have to define. Now the soil of Chaldaea to a great depth beneath the surface is a fine loose earth, similar to that of the Nile Delta. At a few points only on the plain, and that near the Persian Gulf, are there some rocky eminences, the remains of ancient islands which the gradual encroachment of the two great rivers has joined to the mainland of Asia. Their importance is so slight that we may fairly ignore their existence and assert generally that Chaldaea has no stone. Like all great rivers, the Tigris and Euphrates in the upper and middle parts of their courses carry down pieces of rock from their native mountains, but after they enter upon the alluvial ground near the boundary between Assyria and Chaldaea their streams become sluggish, and these heavy bodies sink to the bottom and become embedded in the soil; the water no longer carries on with it anything but the minute particles which with the passage of centuries form immense banks of clay. In the whole distance between Bagdad and the sea you may take a spade, and, turn up the soil wherever you please, you will not find a stone as big as a nut. In this absence of a natural stone something had to be found to take its place, and the artificial material we call brick was invented. The human intellect refuses to give up the contest with nature before the first obstacles that seem to bar its progress; if it cannot brush them aside it turns their flank. The least accident is often enough to suggest the desired expedient. The origin of almost all the great discoveries that are studded over the history of civilization may be traced to some lucky chance. The first inhabitants of Chaldaea fashioned rude kitchens for the cooking of their simple food out of moist and plastic clay, the fires of reed and broken wood lighted on these simple hearths reddened and hardened the clay till it became like rock. Some bystander more observant than the rest noted the change and became the father of ceramics. We use the word in its widest, in its etymological sense. _Ceramics_ is the art of fashioning clay and burning it in the fire so as to obtain constructive materials, domestic utensils, or objects of luxury and ornament.[127]