The general conclusions from this table are, that large and innutritious herbage is, for the most part, destroyed by irrigation, and its place is supplied by grasses; hence, then, the increased value conferred by the regulated action of water is due to an increase in quantity and quality of the grasses, added to a much more certain, as well as early, production of these. Of course the districts best adapted to irrigation will be valleys of denudation, the centres of which are occupied by more or less copious and rapid streamlets. Some of these valleys in the Cotteswolds having been scooped out of the oolitic freestones, have left the spoils of the rock as a gravelly deposit, sometimes on the lias, at others on the fuller’s earth, and then on the Oxford clays; so that, stiff as these soils would be by themselves, they now only tend to throw out the waters by natural drainage, which are again conducted over the porous gravels through which they flow with great regularity; thus fertilizing what would otherwise be but a scanty thin-soil herbage, and to such an extent that early depasturing, haymaking, and later pasturage (_lattermath_) are the rule year by year. These circumstances make water-rights of great value, and which, if not in possession, are secured at a fixed charge per acre; this, however, is usually included in the expenses, which, as before stated, are covered by about 6_s._ per acre. Before concluding this chapter, we must say a few words in reference to flooded meadows. These will be found on the banks of the larger rivers or on streams of sufficient importance to be called rivers, as distinguished from brooks or streamlets. Here the flooding is caused by the water overflowing the banks, as the result of sudden thaws or an unusual quantity of rain. Here then the flood is not under control, and as it may happen at any and all times of the year, the grass may be spoiled by being covered with silt and drifted materials, or even the hay may be carried away by the flood. These river flats, then, have seldom the requisites for carrying on irrigation, although the waters are of course more abundant than those supplied by the smaller streams; for even if we could by embanking so far control the water as to get it over the field when we might wish, yet alluvial flats like those of much of the Thames and Severn would not readily drain. From facts like these it will at once be seen that there is a wide difference between irrigation and flooding; and we have hence endeavoured to separate what is too often confounded. CHAPTER XIV. ON THE LAYING DOWN OF PERMANENT PASTURE. If we reflect upon the fact that much of the meadow of Great Britain is ribbed by the ridge and furrow of former arable culture, we shall conclude that the laying down of land to permanent pasture is an ancient no less than a modern process.