9. That they did put stone to one practical use--the outward casing of their walls and platforms--we have already seen. The blocks must have been cut in the Zagros mountains and brought by water--rafted down the Zab, or some other of the rivers which, springing from those mountains, flow into the Tigris. The process is represented with perfect clearness on some of the sculptures. That reproduced in Fig. 13 is of great interest, as showing a peculiar mode of transport,--rafts floated on inflated skins--which is at the present moment in as general and constant use as it appears to have been in the same parts three thousand years ago and probably more. When Layard wished to send off the bulls and lions which he had moved from Nimrud and Koyunjik down the Tigris to Baghdad and Busrah, (or Bassorah), there to be embarked for Europe, he had recourse to this conveyance, as no other is known for similar purposes. This is how he describes the primitive, but ingenious contrivance: "The skins of full-grown sheep and goats, taken off with as few incisions as possible, are dried and prepared, one aperture being left, through which the air is forced by the lungs. A framework of poplar beams, branches of trees, and reeds, having been constructed of the size of the intended raft, the inflated skins are tied to it by osier twigs. The raft is then complete and is moved to the water and launched. Care is taken to place the skins with their mouths upward, that, in case any should burst or require refilling, they can be easily reached. Upon the framework are piled bales of goods, and property belonging to merchants and travellers.... The raftmen impel these rude vessels by long poles, to the ends of which are fastened a few pieces of split cane. (See Fig. 14.) ... During the floods in spring, or after heavy rains, small rafts may float from Mosul to Baghdad in about eighty-four hours; but the larger are generally six or seven days in performing the voyage. In summer, and when the river is low, they are frequently nearly a month in reaching their destination. When they have been unloaded, they are broken up, and the beams, wood and twigs, sold at considerable profit. The skins are washed and afterward rubbed with a preparation, to keep them from cracking and rotting. They are then brought back, either on the shoulders of the raftmen or upon donkeys, to Mossul and Tekrit, where the men engaged in the navigation of the Tigris usually reside." Numerous sculptures show us that similar skins were also used by swimmers, who rode upon them in the water, probably when they intended to swim a greater distance than they could have accomplished by their unassisted efforts. (See Figure 16.) [Illustration: 15.--EXCAVATIONS AT MUGHEIR (UR).]