The preceding observations, however, have relation to the subject of this article only, inasmuch as they are introductory to what follows. The most beneficial and ingenious improvement that has been made in saws was the invention and introduction of machinery, called saw-mills, which, in woody countries, as well as for delicate and fine veneers, are of the greatest utility; in the former case, wood forms the chief article of commerce where labourers are scarce; in the latter, it may be cut nearly as thin as a sheet of paper. These saw-mills also finish flooring deals, grooved, dovetailed, and planed on both sides, at the rate of two deals, of twenty feet each, in a minute! They are commonly worked in this country by means of steam-engines; in woody countries they are generally erected on the banks of rivers, the water of which propels the machinery. It is said they were invented in Germany, as far back as the fourth century, upon the smaller river Roer; for, although Ansonius speaks of water-mills, for cutting stone, he says nothing of mills to cut timber. The art of cutting marble with a saw is very ancient; Pliny thinks it was invented in Caria; at least, he knew of no place or building, incrusted with marble, older than the palace of King Mausolus, at Helicarnassus. Vitruvius also names the circumstances, although he uses different terms for expressions of the same sense. He commends the beauty of its marble, whilst Pliny speaks of its different kinds: the former viewed it as an architect, whilst the latter inspected it as a naturalist. It also does appear, from other writers, that the harder and precious kinds of stones were cut in the same manner; as Pliny speaks of a building adorned with agate, cornelian, lapis-lazuli, and amethysts. Yet there is no mention made of mills for cutting wood; or, admitting they had been invented, it is probable they shared the fate of many other useful inventions,--had been forgotten, or else some considerable modern improvement had been made in their construction. Since the period of the first invention, they have been erected in various parts of Europe and America. There appears to have been one erected in the vicinity of Augsburg, as early as 1337; at Erlinger, in 1417.