The other structures (3, 4, 6, 7) served industrial purposes. No. 4 (fig. 5) contained a hypocaust and was perhaps a workroom and drying shed. At 6 were ill-built and ill-preserved rooms, containing puddled clay, potsherds, &c., which declared them to be work-sheds of some sort. Finally, at 3 and 5 we have the kilns. No. 3 was a kiln 17 feet square, with a double flue, used (as its contents showed) for potting, and indeed for fine potting. No. 5 (figs. 8, 9) was an elaborate 'plant' of eight kilns in an enclosure of about 55 x 140 feet. Kilns A, B, F, H were used for pottery, C, D, E for tiles, F for both large vessels and tiles; the circular kiln G seems to be a later addition to the original plan. The kilns were thus grouped together for economy in handling the raw and fired material and in stacking the fuel, and also for economy of heat; the three tile-kilns in the centre would be charged, fired, and drawn in turn, and the heat from them would keep warm the smaller pottery-kilns round them. The interiors of the kilns contained many broken and a few perfect pots and tiles; round them lay an enormous mass of wood-ashes, broken tiles and pots, 'wasters' and the like. The wood-ashes seem to be mainly oak, which abounds in the neighbourhood of Holt. The kilns themselves are exceptionally well-preserved. They must have been in actual working order, when abandoned, and so they illustrate--perhaps better than any kilns as yet uncovered and recorded in any Roman province--the actual mechanism of a Roman tile- or pottery-kiln. The construction of a kiln floor, which shall work effectively and accurately, is less simple than it looks; the adjustment of the heat to the class of wares to be fired, the distribution of the heat by proper flues and by vent-holes of the right size, and other such details require knowledge and care. The remains at Holt show these features admirably, and Mr. Acton has been able to examine them with the aid of two of our best experts on pottery-making, Mr. Wm. and Mr. Joseph Burton, of Manchester. [Illustration: FIG. 8. PLAN OF KILN-PLANT AT HOLT (SEE p. 34, and FIG. 9) (Except at kilns F, G, the letters on the plan are placed at the fire-holes. In kilns A, B a small piece of the kiln floor (on which the vessels were placed for baking) is shown diagrammatically, to illustrate the relation between the hot-air holes in the floors and the passages in the underlying heating-chambers)] [Illustration: FIG. 9. RESTORATION OF THE HOLT KILN-PLANT, SHOWING THE FLOORS ON WHICH THE TILES OR VESSELS WERE PILED FOR BAKING (p. 18) The letters ABCDE are placed at the mouths of the stoke-holes of the respective kilns. Kilns ABDFH were used for pottery, CDE for tiles, F for large vessels and for tiles; G seems an addition to the original plan.]