But the most important cause of submergence is the gradual compression or consolidation of the lake-bed due to the increase of its sediment. The depth of this increase at Lochlee, at least since the gangway was laid, was found to be not less than 10 feet. Independent altogether of any chemical changes going on in the sediment, however gradually formed, its own weight must have acted very considerably in pressing the lower strata into less bulk. Its accumulated depth, however, is far from giving a correct indication of the rise in the bed of the lake; in fact, 10 feet of silt might not raise the latter to half this extent. Another thing, which must not be forgotten in this discussion, is the subsidence which takes place after bogs and marshes are drained. This is a fact well known to those conversant with the effects of drainage. In the _Old Statistical Account of Scotland_, vol. xi. p. 163, I find it stated that in three years after the drainage of Kinordy Moss, its surface sank 3 feet; and Sir George Grant Suttie, writing of a drained marsh at Balgone, says that after drainage its level sank from 3 to 4 feet (see footnote, page 249). Bogs are in fact like sponges saturated with water, swollen to such an extent that they occupy a much larger space than their solid materials would otherwise do. It will also be remembered (page 191) that, after the last and more careful drainage of Loch Buston, some five years ago, the subsidence of the _Knowe_ was sufficiently noticeable to attract the attention of the farmer. To assign more accurately to these agencies the respective amount of subsidence due to each is impossible, but that their combined effect is sufficient to account for the total submergence of the principal lake-dwellings hitherto examined is proved by the measurements and observations made at Lochspouts (page 168), which show a minimum result of 10 feet. If the above reasoning be correct, little importance remains to be attached to the rising of the waters as a cause of submergence, even in the exceptional circumstances where the agencies that produce this effect, such as the destruction of the forests and the increase of peat bogs, are known to have been in operation. It occurs in localities where the outlet is level and the flow of water sluggish. Those of the Irish writers who have taken notice of the phenomenon generally assign it to this cause. Sir W. R. Wilde thus refers to it: "We likewise learn from their recent submerged condition how much water had accumulated on the face of the country since their construction, probably owing to the great decrease of forest timber and the increased growth of bog. From the additions made to the height of the stockades, and also from the traces of fire discovered at different elevations in the sections made of these islands, it may be inferred that the rise of the waters commenced during the period of their occupation."--(Wilde's _Catalogue_, p. 221.)