These great marshes and reed-beds are full of interest to naturalists. The Fens of Lincolnshire and the Norfolk Broads show the way in which water plants keep hold of the worn and travelled rubbish of the hills, and prevent most of it from becoming useless, barren sea-sands. These places, however, like the sudd of the Nile, and the Roman "Campagna," have an evil reputation so far as climate is concerned. This used to be the case even in lower Chelsea, in London (where snipe were shot not so very long ago). It is as if Nature had desired to do her own work in peace and without being disturbed, for fever, ague, mosquitoes, and malaria are very common. Yet a certain number of people always live in such places. In France, e.g., the leeches in the great marshes near the Landes form a source of riches. Such reeds also are or were the home of the hippopotamus, crocodile, and other extraordinary animals. The extinct British hippopotamus no doubt found in the Chelsea or other marshes a home as congenial to its tastes as is the sudd of Egypt to its living descendants or allies. In other places the enormous quantities of water birds, myriads of ducks, geese, swans, regiments of flamingoes, snipe, and the like, have called into existence peculiar kinds of industry in fowling and netting that are not without importance. The decoys in the Fens yield hundreds of birds for the London market, and the duck-punts with their huge guns also bring in quantities of wild fowl. But all this industry is very trifling compared with that of Phragmites and its associates, who have strained from the water of the Thames most of the ground on which London now stands. CHAPTER XVII ON GRASSLANDS Where is peace?--Troubles of the grass--Roadsides--Glaciers in Switzerland--Strength and gracefulness of grasses--Rainstorms--Dangers of drought and of swamping--Artificial fields--Farmer's abstruse calculations--Grass mixtures--Tennis lawns--The invasion of forest--Natural grass--Prairie of the United States, Red Indian, Cowboy--Pampas and Gaucho--Thistles and tall stories--South Africa and Boers--Hunting of the Tartars--An unfortunate Chinese princess--Australian shepherds. Where should one seek for peace on earth? The ideal chosen for one well-known picture is a grassy down "close clipt by nibbling sheep," such as the fresh green turf of the South Downs. Others might prefer the "Constable country," near perhaps the famous "Valley Farm" of which the picture now hangs in the National Gallery, and especially in early spring. At any rate, once seen, one remembers for ever afterwards those glossy-coated, well-fed, leisurely cows grazing hock-deep in rich meadows full of bright flowers and graceful grasses, through which there winds a very lazy river bordered by trim pollarded willows. The charm of the South Downs and of Constable's meadows depends upon their peaceful quiet, and the absence of any sign of the handiwork of disturbing man.