Mark felt here the same fear that others spoke of feeling in the forest. There was a presence here, and it was malign. He found himself looking back over his shoulder again and again, and determinedly paddled ahead. Soon he would stop and make some sketches of the buildings he could see from the river. Probably he should make some token explorations on foot, he thought reluctantly. He paddled more slowly and examined a grove of trees. They were so badly formed it was hard to determine what kind of trees they were. Aspens, he decided. He tried to imagine their roots searching in the concrete and metal beneath the streets for sustenance, finding only more concrete and metal.

But there had been trees in Washington, he thought, paddling harder to avoid a large, ragged chunk of ice. Those trees had been normal-looking, but these… They were less than half full size, misshapen, their branches few and grotesquely twisted. Abruptly Mark pulled up. Radiation, he thought with a chill. This is what radiation poisoning did. Before his mind's eye appeared descriptions and photographs of various kinds of animal and vegetable life deformed by radioactivity.

He turned the canoe and raced back downriver to the juncture with the Delaware. He still had several hours before darkness forced him to stop. For a moment he hesitated, then turned northward once more, this time keeping a wary eye open for deformed plant growth, as well as for chunks of ice, which had become more numerous.

He passed one more place with badly deformed plant life. He kept to the far side of the river and continued to paddle.

Philadelphia went on and on, the ruins more or less uniform. Occasionally there were blocks of buildings that seemed virtually untouched, but now he suspected that was because those areas had been blocked off when they became radioactive. He didn't investigate any of them. Most of the immense buildings were skeletons, but there were still many standing, enough to make a full-scale expedition worthwhile, if the buildings were not contaminated. He knew that problem would have to be solved by Barry or his younger brothers. He continued on. The forests were taking over again, and the trees were well developed here, thick, luxuriant; in some places where the river narrowed, the canopies met overhead, and it was like passing through a tunnel where only his paddle in the water made a sound and the rest of the world held its breath in the twilight stillness.

There was another puzzle here, he thought, studying the banks of the river. The flow was very swift, but the water was low and the banks in places rose several feet to the land above. The river could have been partially dammed; he knew he would have to find out before he returned to Washington.