A biographer's great challenge, when the subject is genius, is to trace the alchemy that produced the gold. It is a special challenge in the case of writers, since even the most gifted require longer seasoning than, say, physicists or composers. History records no Mozarts of the quill.

John Lauber's strategy in this estimable book -- one of many that will betide us on the 150th anniversary of Mark Twain's birth -- is painstaking documentation. He follows Samuel L. Clemens from his days as a 14-year-old newspaper apprentice in Hannibal, Mo., to the threshold of his arrival as a celebrated writer with the publication of "The Innocents Abroad" when he was in his early 30s. In between there are revealing glimpses of his parents (his father was constantly down on his luck, and the family migrated from house to ever-smaller house); of the young Clemens' chance observation of his father's autopsy through a parlor keyhole; of the "family lands" back in Tennessee, which, though of no cash value, provided a certain anchor to the Clemenses' shabby gentility; of the successful but abbreviated career (two years) as a Mississippi steamboat pilot; of Twain's life during the Civil War years in the mushrooming mining towns of Nevada and California.

Lauber's approach is based, apparently, on the mildly behaviorist premise that the "making" of a writer may be understood environmentally -- data omnia vincit -- never mind that crucial links between experience and the development of a sensibility can be elusive and less than self-evident.

A second, perhaps more fruitful, premise is that the old cliche' about Twain's "dual" character, first emphasized by Van Wyck Brooks and prolonged even by his latest biographer, Justin Kaplan, is misleading. Samuel Clemens and Mark Twain, Lauber insists, are of a piece. The supposed tension between the solid bourgeois citizen and the free-spirited writer simply wasn't there or at least wasn't very important.

Kaplan's justly celebrated biography of some years ago, which reinforced the "dualist" theory, took up Twain's story after the presumably formative early years. Lauber aims, then, to fill a gap, and he fills it in a workmanlike way. Unfortunately, these chronicles frequently drag and droop, taking on the tone of a travelogue, an itinerary of Twain's movements (he was always restless and nomadic). The connective tissue between experience and development is missing. "The Making of Mark Twain," in short, tells less about the making than about the moving about.

Perhaps that is unavoidable. Despite the implication of the title, several facts about the Mark Twain described here suggest his character was unfinished. It is, for example, a mystery why Twain all but ignored the Civil War, which broke out when he was a vital young man of 25. He would later be an angry political activist, opposing the Spanish-American War and its bloody Philippine aftermath, but nothing in the War of the Secession seems to have engaged his passions. That he grew up in a border state whose families were often fiercely divided may extenuate but does not explain this. Young Clemens enlisted briefly in a militia unit, but it soon disbanded. He then decamped to Nevada, of which his rolling-stone older brother, Orion, had been appointed territorial secretary. Meanwhile, tens of thousands of young Americans were chasing one another across the bloody soil of Virginia, Maryland, the Carolinas, Tennessee and Pennsylvania -- and in the trans-Mississippi region as well. What did he think of this pivotal conflict, and what effect did it have on him?

William Dean Howells said that in later life Twain was radically "de-southernized," scornful of the magnolia mentality. Lauber pauses briefly over this interesting conflict of regional loyalties during Twain's years as a western journalist.

The other evidence of unfinished character is this: At the time he was wooing Olivia Langdon, later to be his beloved wife "Livy," Clemens/Twain was still strikingly deferential to Victorian conventionalities. He might privately be ribald and profane, as friends told it, but he declined to recommend Shakespeare to his virginal sweetheart, at least until it could be "purged of its grossness." How much of this was pose, how much good manners, how much unsettlement of character, it is no doubt hard to guess. Again, however, Lauber resists a powerful temptation to explore and analyze.

In any event, it is a strain to recognize in the Mark Twain who emerges from this supposed "shaping" even a trace of the nature that would make him, in Howells' term, "the Lincoln of our literature." Twain's response to so many subjects was burlesque -- often sophomoric and tiresome. It was far indeed from the fiendishly on-the-mark satire and misanthropy of his later writings. Even Twain seems to have sensed it. Of his first big success, the story of the "celebrated jumping frog" (1865), he marveled that easterners would admire and reprint "a villainous backwoods sketch."

For readers seeking reliable information about Clemens/Twain, tidily arranged, Lauber's book is excellent. Its shortcoming is timidity. The author seems to me to shrink, too fastidiously, from seeking the catalysts of transformation that turned raw frontier talent into genius. He clearly assumes such a transformation and assumes the experiences of young manhood had much to do with it. Just what they had to do with it, however, he is content to leave the reader to infer.