What can you infer about Tom Walker from his reaction to the swamp and to his grisly discovery of the skull?

From his reaction to the swamp and the skull, we can infer that Tom Walker is not easily intimidated or swayed by public opinion and popular superstitions. We can also infer that Tom Walker has a rather apathetic outlook on life: the split skull has an Indian tomahawk lodged deep in it, but this fails to inspire much of a reaction from Tom. He is merely irritated at finding something that can't add to his wealth, and he kicks it away.

Any one but he would have felt unwilling to linger in this lonely melancholy place, for the common people had a bad opinion of it from the stories handed down from the time of the Indian wars; when it was asserted that the savages held incantations here and made sacrifices to the evil spirit. Tom Walker, however, was not a man to be troubled with any fears of the kind.

Earlier in the story, he takes a shortcut home through the swamp. Most people avoid the area, but Tom feels quite at home in the eerie surroundings. The text tells us that the swamp is thickly grown with giant pines and hemlocks, and this keeps the swamp in darkness even during the day. We are also told that the swamp is full of "dark and stagnant pools," "pits and quagmires," and is partly covered with "weeds and mosses." Beneath the green mosses lie a layer of "black smothering mud." Altogether, it isn't the kind of place most people would prefer to find themselves in.

As for Tom, his main focus is on increasing his personal wealth, so neither superstitions nor genocidal massacres inspire much emotion from him.