You'll notice on your left as we begin this guided tour of Jean Shepherd's mind a strange-looking black rock that is all scratched up. This is Mr. Shepherd's sense of humor. Yes, it is rather gnarled and weatherbeaten. It's been used for quite some time. Over here on the right, if you look closely, you can make out a tall, spiraling object that is quite sharp at its pointed end. That is Mr. Shepherd's cynicism. The smooth surface is something Mr. Shepherd bas been honing for many years. Now, if you come this way, we'll take a peek at Mr. Shepherd's liver. Kindly observe it is the liver of a man who is filthy rich at last. Beginning this week, Jean Shepherd will embark on his own tour. You're welcome to come along for the ride. The price of admission is laughter. Leave that excess baggage of seriousness behind. You won't need it anyway. The tour is called "Jean Shepherd's America," airing over PBS, WTTW Channel 11, at 12:30 p.m. Saturdays, about as idiotic a time to schedule this series (couched between the kiddie cartoons and the kung fu movies) as you can imagine. But then again, maybe the programming department at WTTW has its own warped sense of humor. This 13-part series is a revival of Shepherd's last cross-country tour 12 years ago. This time around Shepherd spreads his whimsy from coast to coast, but he takes exception to any suggestion that his tour of America is the counterculture's answer to Charles Kuralt. "Oh, no," he said. "I don't do travelogues. I'm a humorist, that's what I do. Besides, I never thought of Kuralt as being funny, at least he doesn't think he is. "I have nothing to do with Kuralt any more than Johnny Carson is a mainstream Merv Griffin." Shepherd said. To prepare for this series, which takes him wandering through Florida's intercoastal waterway, to Guam, to Milwaukee, to the Okefenokee Swamp, Shepherd does absolutely nothing. "I'm not interested in facts and figures," said the Chicago-raised Shepherd. "My shows are about ideas rather than places. It comes out of my interests. It's like asking Picasso, 'How do you decide to paint these pictures?' " In this series, Shepherd's interests run the gamut from the lore of beer to the meaning of the word "hometown," from the mystique of wealth to tourism, the old South and cars. Perhaps you wouldn't ask Picasso why he paints, but then again ... Why did he paint all that stuff? And what motivates Jean Shepherd to think the way he does? ''It's all madness," he said with a laugh. "No matter what part of life you take it's a shaggy dog story. Don't expect a happy ending, friends. In fact, don't expect an ending. "That's the way I see life," Shepherd said of the one constant thread through his plays, books, film scripts, stand-up humor act and "America." "I'm not going to stand in front of a glacier and get very pompous about how long the glacier is; that's the Kuralt bit," Shepherd said. "I'll wander along the glacier and all of a sudden, out in the wilderness, I will find a Colt .45 [beer] can." Shepherd admits his deadpan humor remains an acquired taste for some people. "Humor is the most personal of all human emotions," he said. "It's much more personal even than sex and people write manuals about sex." During this series, the viewer will see Shepherd in a variety of roles, playing a man of extreme wealth, a beer guzzler and so forth. And Shepherd said he worries the audience will think he is playing himself, rather than a character. "Television is a literal medium today," he said. One "America" segment Shepherd is proud of is the piece done on Chicago, in which the city is used as a metaphor to discuss the meaning of the word: "hometown." The segment will open with Shepherd's low, melodic voice extolling the virtues of hometown life. As he talks about the general store, the camera pans Marshall Field's; all he lyrically recalls the old swimming hole, we see Lake Michigan. "It was so polluted when I was a kid, you could walk halfway to Milwaukee before you started to sink in," follows Shepherd's narration. Shepherd, who said he grew up in the St. Louis Street/Irving Park area as well as Hammond, Ind., also takes on the traditional Chicago North Side vs. South Side rivalry of which the Cubs and the White Sox lead the respective charges. "It rains year in, year out, on the South Side," said Shepherd. For Shepherd, who once did television and radio commercials for the Sun-Times before branching out in other fields, there are few things in life he takes seriously. "Well, there is the IRS," he said somberly. "I've tried to write them funny letters. "The things in life that are really serious are the things which tend to dampen the spirit and the IRS is certainly one of the great spirit dampeners of all time.