Those Nights on the Harlem Rooftops : JAZZ, <i> By Toni Morrison (Alfred A. Knopf: $21; 226 pp.)</i>

“Jazz” is a half-waking dream on a lumpy corncob mattress. Its voices shift, almost in a single sentence, from down-to-earth to intensely poetical. It alternately asserts, and transforms what it asserts. Each shift--each page, virtually--begins with a tangible jolt of discovery, and dissolves, making way for the next shift and dissolution. It can be difficult to follow, yet immensely exhilarating. We raft down Toni Morrison’s white water, get mired when it sinks into passages that run too deep underground, and float off when it breaks into the open.

“Jazz” has fewer undergrounds than did “Beloved,” its predecessor. To my mind, it surpasses it. Nearly as heart-stopping in its intensity, “Jazz” is on the whole a freer and sunnier book.

In part, this is because of its theme, a kind of sequel to that of “Beloved.” From the darkness of slavery and its nightmare aftermaths, it moves into the glitter, the exaltation and the pain of the turn-of-the-century migration of black people from the rural South to the cities of the North.

The theme is played out principally in the story of Joe and Violet Trace, a Harlem couple who moved north in 1906. Set 20 years later, when they are in their settled and comfortable 50s, it tells how they shatter and heal after an act of passion and violence.

Morrison stories, like the blackbirds that fly through Joe’s memories, never come singly. “Jazz” ranges back into the haunted and still blood-stained Virginia countryside of the 1890s. It relates death and disappearance, and the struggle of black people to survive and scratch out a living under a brutal white hegemony. And yet it is their struggle and their living, and that is the difference from the times of “Beloved.”

Freedom is a banked ember for the abused sharecroppers but, among other things, it is freedom to get on a train. And when, at 30, Joe and Violet finally do; and when, north of Delaware, the Jim Crow green curtain that divides the dining car is pulled open, the ember flares into a blaze. “Jazz” is the story of the blaze, of its magnificence. These were the years when Harlem meant hope, excitement, empowerment, choice, the material flash and glisten of city life and a modest prosperity--and the destruction it brings about at the same time. Joe and Violet partake of both.

Everything bleeds into everything else. Morrison’s events all father ghosts, and by no means are all of them tragic. The suicide of Violet’s mother after white men break up her home lives on in the long state of depression she goes through later. Her grandmother’s fierce, life-defying smile lives on in a fierce smile of her own. The disappearance of Joe’s mother “without a trace”--the neighbors use the phrase; child Joe assumes that he must be “Trace” and adopts it as his surname--erupts in his middle age as he desperately pursues a teen-age lover. But the laborious will to survive he learned as a young farm worker, and the moral strength, imparted by an old black hunter, come with him as well, and enable him to survive his tragedy.

So much for the theme and, very vaguely, the story. But even if developed in 10 times the detail, they would barely be the skeleton. They would be an opera’s libretto without the music. “Jazz” is no arbitrary title, and not simply a motif. Jazz is the world of Joe’s young lover, and musicians play it in the cool evenings on Harlem’s rooftops. But much more than that, it is the very form, voice and core of this wonderful book. Here is the first paragraph; it sums up the story of Joe and Violet, but it does it as a trumpet blares a theme that is then unwoven, rewoven, tickled and teased, built up and tossed around for as long as anyone still feels like playing:

”. . . I know that woman. She used to live with a flock of birds on Lenox Ave. Know her husband, too. He fell for an 18-year-old girl with one of those deep-down, spooky loves that made him so sad and happy he shot her just to keep the feeling going. When the woman, her name is Violet, went to the funeral to see the girl and to cut her dead face they threw her to the floor and out of the church. She ran, then, through all that snow, and when she got back to her apartment she took the birds from their cages and set them out the windows to freeze or fly, including the parrot that said, ‘I love you.’ ”

Each of those phrases is expanded, elaborated, improvised upon. Each links up with the story and its larger themes. Morrison’s vision of the city as joyful liberation--standing in the north-bound railroad car, Joe and Violet dance to its jolts--is coupled with its denaturing, destructive power. For love, Joe ruminates, the city substitutes desire; for air, it substitutes breath.

Take the birds. Freed from the South’s back-breaking cycle of labor--in both senses--Violet refuses to have children. While Joe earns a good living as a waiter in a downtown hotel, and sells cosmetics on the side, she bustles around Harlem as a home hairdresser. Then childlessness catches up with her, sending her into silent depression. At home she talks only to her birds and a doll she keeps under the bed.

When her silence, the city’s offer of easy pleasure and Joe’s own demons drive him to take up with Dorcas, the teen-ager, and then to shoot her, Violet’s despair sends her on a rampage that ends with her birds. The parrot goes out on the window ledge, but since he can’t fly he stays there, looking in. Day after day, he squawks “Love you” through the windowpane until he topples off and dies.

There is sharp grief there, the fall of a world in the fall of a parrot. Morrison can play grief this small; she can play it much larger. In 1880 or so, Violet’s mother, Rose, sits in her cabin clutching her empty coffee cup while bailiffs remove the furniture piece by piece. They remove the table at which she is sitting, then they slowly tip her chair forward until she topples onto the floor. The cup rolls away. And the neighbors come consoling:

“He ain’t give you nothing you can’t bear, Rose. But had He? Maybe this one time He had. Had misjudged and misunderstood her particular backbone. This one time. This particular spine.”

Amid the pain, there is a beauty that Morrison achingly conveys: of the countryside and the deep loyalty of the black farmers to the land and each other; and of Harlem in its glory days. There is a humor that braids into the pain and goes as deep.

The black sharecroppers are burned out to free them to harvest the white man’s cotton, a bumper crop after years of drought: “Softer than silk and out so fast the weevils, having abandoned the field years ago, had no time to get back there.” Young Violet, an itinerant cotton-picker, sleeps out in the fields one night. Something falls from the tree beside her. “The thump could not have been a raccoon because it said Ow.” It was the first meeting with Joe, who had been sleeping in the branches.

The stories fan out through Harlem at a time when drink, sex, disrespecting the elders, and the knife fight were the measure of social decay; when church groups held bridge parties, and neighbors strolled and sat out on the stoops. They fan back to the ghosts in the South. There is a young man brought up as white by his rich mother, who learns his father is black and goes to confront him. There is Joe’s wandering mother who takes to the woods, lives in a cave and is attended by flights of blackbirds.

And the story of Joe and Violet, which starts gentle and then turns bloody and dark, turns gentle once more. After the shooting, a turbid, confused affair, nobody cares to identify Joe to the police. For weeks, he sits in his room weeping and inert; and it is Violet, after her rampage and roused from her lethargy, who begins to rouse him and mend their life.

Their story could have been either a tragedy or a melodrama, with appropriate climactic endings. But Morrison has written a book that ruminates and discourses, that wanders into climaxes and wanders out of them, that follows its riffs through pain and celebration, that moves all the time while neither leaving the past nor disappearing into the future; that is, in her word, jazz.

In Toni Morrison’s “Jazz,” Joe and Violet arrive in New York City in 1906:

Like the others they were country people, but how soon country people forget. When they fall in love with a city, it is forever and it is like forever. As though there never was a time when they didn’t love it. The minute they arrive at the train station or get off the ferry and glimpse the wide streets and the wasteful lamps lighting them, they know they are born for it. There, in a city, they are not so much new as themselves; their stronger, riskier selves. . . .

What they start to love is the way a person is in the City; the way a schoolgirl never pauses at a stoplight but looks up and down the street before stepping off the curb; how men accommodate themselves to tall buildings and wee porches, what a woman looks like moving in a crowd, or how shocking her profile is against the backdrop of the East River. The restfulness in kitchen chores when she knows the lamp oil or the staple is just around the corner and not seven miles away; the amazement of throwing open the window and being hypnotized for hours by people on the street below.

Little of that makes for love, but it does pump desire. . . . There is no air in the City but there is breath, and every morning it races through him like laughing gas brightening his eyes, his talk and his expectations. In no time at all he forgets little pebbly creeks and apple trees so old they lay their branches along the ground and you have to reach down or stoop to pick the fruit.