Since then their successors have used the land for farming and for other purposes. In using it they have changed it, and the changes have registered in the river system that drains it. For land, water, vegetation, wildlife, minerals, and men's habits are not separable from one another in the natural frame. So that if the early planters, using methods of hoe tillage scarcely less primitive than those of the Indians, mined the Tidewater soils for tobacco production in a way that required new fields every few years, one result was that those soils tired and thinned and finally stopped supporting the social magnificence that had grown up there, for production and prosperity moved inland and west. And another result was that the Potomac estuary itself grew shallower and different with the silt that washed down off the land, and many a tributary bay that once served as harbor for oceangoing ships is now a rich, reedy marsh with a single narrow gut of shoal water wandering down across it to the Potomac. And if later generations of men cut down the forests on the mountains in the western Basin, and fire followed the cutting, thousands of years of soil washed down from those slopes too to change both mountains and river, and elk and panther vanished. And if along the Potomac's North Branch there was once a fine coal boom, there is now the boom's legacy in the form of gray dour towns and dark sad streams corrosive with mine acids. And if old Alexandria and Georgetown and all the land around them have burgeoned into one of the nation's great cities, there has been a price to pay for that also. The stately upper estuary on which they front is often turbid with silt and sometimes emerald green with algae nourished on sewage and other septic riches, and the hills stretching back from the river are spiky with tall buildings linked by urban and suburban clutter, where life lacks the natural elbow room that the old Tidewater folk--planters and yeomen and bondsmen and slaves alike--were able to take for granted. These are facets of an Age of Problems, of course. They and other related troubles have been growing apace lately as men have grown in numbers, in the demands they make on the natural environment that shaped and nourished their species, and in their technological power to enforce those demands. The troubles pose a threat to men of flavorlessness and grayness and the loss of essential meanings, a threat of diminished humanity. For dependence on that environment, intricate and deep-rooted, psychological as well as physical, has not grown less with the human advance toward power and sophistication.