The practice of enclosing open land had almost ceased before the death of Elizabeth. There was some enclosing under James I, but it seems to have been quite exceptional. In the main, those common pastures and open fields which had not been enclosed by the beginning of this period, probably one-half of all England, remained unenclosed till the recommencement of the process long afterward. Sheep farming gradually ceased to be so exclusively practised, and mixed agriculture became general, though few if any of those fields which had been surrounded with hedges, and come into the possession of individual farmers, were thrown open or distributed again into scattered holdings. Much new land came into cultivation or into use for pasture through the draining of marshes and fens, and the clearing of forests. This work had been begun for the extensive swampy tracts in the east of England in the latter years of Elizabeth's reign by private purchasers, assisted by an act of Parliament passed in 1601, intended to remove legal difficulties. It proceeded slowly, partly because of the expense and difficulty of putting up lasting embarkments, and partly because of the opposition of the fenmen, or dwellers in the marshy districts, whose livelihood was obtained by catching the fish and water fowl that the improvements would drive away. With the seventeenth and early eighteenth centuries, however, largely through the skill of Dutch engineers and laborers, many thousands of acres of fertile land were reclaimed and devoted to grazing, and even grain raising. Great stretches of old forest and waste land covered with rough underbrush were also reduced to cultivation.