4. _Increasing wealth and new labor make possible the increase of the agents that appear most nearly fixed in supply._ When the need arises men turn to new enterprises. The reclaiming of land in Holland is a striking but far from isolated example. Among the larger undertakings of this kind are the draining of the Haarlem Lake in 1840-58, by which 40,000 acres of rich land were made available, and the draining of the Zuyder Zee, which is adding 1,300,000 acres. Though there have been many minor undertakings of the kind, the area reclaimed is relatively small compared with the whole area of the land in the world used for agricultural purposes. There are still great areas of fens, swamps, and marshlands, such as those on the Jersey coast in this country, which with moderate effort could be reclaimed. While the possibility must be recognized, the increase of the area of available agricultural land by means of such physical changes is relatively small. [Sidenote: And by the work of pioneers] The work of the pioneer, as a producer of a supply of land, is, however, of the greatest importance. The pioneer annexes new areas to the economic world and to the market in which he has lived. This is recognized of late by writers that perhaps do not fully mark its significance to economic theory. The work of the explorer and prospector is that of a producer of mineral resources, and daily market quotations reflect the changes in "the supply" of these natural stores. [Sidenote: Successive utilization of various grades of agents] 5. _Limitation of the supply appears first in the better qualities, and efforts to increase wealth are then directed to making available the poorer grades._ Great quantities of the poorer grades of wealth, even of those things that are relatively fixed in supply, lie unused. Great areas on the edge of civilization still await the pioneer, the prospector, and the miner. Here is a source of wealth and a field for enterprise. The growth of society may cause some of the poorer agents in time to become the best. When men crossed the ocean to settle on Manhattan Island, it was a wilderness; but the growth of commerce has caused the land in New York city to become more valuable than that in London. Changes are still in progress, for of late the smaller ports to the south have increased their trade at a more rapid pace than New York has. [Sidenote: Goods ranged on a scale of increasableness]