Emma Alice Mills, agt ll, of Austell, Ga., for her question:

What exactly are watersheds?

The rain that falls upon the land follows an orderly destiny. some of it sinks into the soil to quench the thirsty plants. some evaporates and some runs to join waterways that finally reach the sea. The networks of runaway rains must obey the geography of watersheds.

All river systems are directed by the ups and downs of the land, for water must flow downhill on its way to the sea. The geography of a continent is often subtle and a land mass may be tipped in slopes too gentle for the human eye to notice. slight humps or ridges often run north and south or east and west almost all the way across a continent.

These geographical features may be hard to spot, but they have a very definite effect upon the rivers. We call them continental divides and they divide the rivers, making them flow in opposite directions. Our famous Continental Divide runs north and south through the western mountains. Many mountains around it are higher, but this ridge marks the high point of two continental sections, one sloping eastward and one westward.

Such a divide is called a watershed. The rain that falls upon it is divided and sent in opposite directions. some joins the rivers flowing eastward across the plains. some joins the mountain streams flowing to the west. Another watershed divide runs east and west across North America. On one side of it rivers flow northward to the Arctic, to Hudson Bay and the Gulf of saint Lawrence. The opposite sidte directs the streams that flow southward to feed the Mississippi.

However, a divide is not the only geographical feature called a watershed. The term also may be applied to the drainage area of a great river system. The Amazon and its tributaries drain a major part of south Africa and this vast drainage area may be called a watershed. Perhaps, you might think, the geographers are confused and these different types of watersheds should have different names.

But if you figure the shape of the land you will see that the divide watershed and the drainage watershed are closely related. In both cases certain continental slopes shed or guide the rain waters to flow in certain directions.

The drainage system of a great river is a vast network of streams. On a flat map the twining rivulets seem to meet by accident. This is because  they bend and turn about hilly heights in their downward paths. There is a general pattern in the network and the pattern is dictated by the slope of the land. The Amazon flows along a wide valley running from west to east. Its watershed is fed by streams wandering down land sloping upward to the north and south.