When we examine as a whole the character of the lacustrine settlements which have hitherto been discovered, it may, in fact, be perceived that those who built them proceeded on two different systems of construction; either, they buried the piles very deeply in the bed of the lake, and on these piles placed the platform which was to support their huts; or, they artificially raised the bed of the lake by means of heaps of stones, fixing in these heaps somewhat large stakes, not so much for the purpose of supporting the habitations themselves as with a view of making the heaps of stones a firm and compact body. [Illustration: Fig. 148.--Section of the _Ténevière_ of Hauterive.] This latter mode of construction is represented in fig. 148, taken from a design given by M. Desor in his remarkable work 'Les Palafittes.'[33] One or the other of these modes of construction was employed according to the nature of the bed of the lake. In lakes with a muddy bottom, the first plan could be easily employed; but when the bed was rocky, it was necessary to have recourse to the second. This is the reason why on the northern shore of the Lake of Neuchâtel, where the banks of limestone come very close to the surface, a comparatively large number of _ténevières_ may be observed. These are the facts as generally noticed, especially in wide and deep lakes; the edifice, however, was not always constructed in this mode. In marshes and small lakes, which have now become peat-bogs, another system was frequently applied, a remarkable instance of which is furnished by the peat-moss at Wauwyl. In this locality were found several quadrangular spaces very distinctly enclosed by piles, between which were raised as many as five platforms one above the other. These piles are naturally very long, and some are buried as much as seven feet in the solid ground--an operation which must have required an enormous amount of labour. The intervals between the platforms are filled up with boughs of trees and clay, and the floors themselves are made in nearly the same way as those we have before mentioned. The lowest rested directly on the bed of the lake, and on the upper one the huts were placed. It is sometimes the case that these heaps of stones rise above the water; they then form perfect artificial islands, and the habitations which covered them are no longer, properly speaking, dwellings on piles. Of this kind is the station on the Lake of Inkwyl in Switzerland; of this kind, also, are the _crannoges_ of Ireland, of which we shall subsequently make special mention. Some of these artificial islands have braved the destructive action of ages, and are still inhabited at the present time. M. Desor mentions the Isle of Roses in the Lake of Starnberg (Bavaria) which has never been known to have been unfrequented by man; it now contains a royal residence. Let us revert to the mode of construction of the aquatic dwellings of Switzerland.