DON'T BE TOO SURE that you have read Thoreau. Those of us who encountered Walden in school or dipped into A Week on the Concord and Merrimack Rivers will only have scratched the surface, even though these were the only books Thoreau wrote that were published in his lifetime. Standing beyond them and all Thoreau's other published writings like a range of distant mountains lie the two million words of the Journals (first edition, 1906), which began on October 22, 1837 (" 'What are you doing now?' he asked. 'Do you keep a journal?' So I make my first entry today"), and ended November 3, 1861, with a last entry: "All this is perfectly distinct to an observant eye, and yet could easily pass unnoticed by most. Thus each wind is self-registering." The first passage records a conversation with Thoreau's mentor Emerson; the last, a response only to the writer's need to record the particular way heavy rain had eroded a railroad causeway. Thoreau's thought, as William Howarth demonstrates, progressed in this direction over the intervening 24 years, broadly speaking, from metaphor to simile.

I wonder if anyone has read Thoreau with more care than Howarth. The Book of Concord might serve as a model for how to relate the vicissitudes of a life, inner and outer, to the vast output of a writer's dedication to the written record of it. Though Thoreau traveled as widely and adventurously as most of his contemporaries (Canada, Maine, New Hampshire, New York, Cape Cod, and Minnesota in a last desperate try to find a climate to aid his tuberculous health), he was perceived as a stay-at- home, "the leader of a huckleberry party," as Emerson persisted in misconstruing him. He also traveled, while stationary, a very great distance in the many-volumed journal he referred to as "the Book of Concord." From it he drew nearly everything he wrote in his maturity. Journal entries piled up from field notes; heaps of material for books piled up in journal entries; books emerged from their cannibalization, through Thoreau's condensation and rewriting.

He was a writer of formidable digestive power. The journals for a two-week trip in 1839 with his brother on the Concord and Merrimack Rivers and up Mount Washington contracted into A Week on the Concord and Merrimack 10 years later. Thousands of pages of the journals of his two-year stay on Walden Pond in 1845-1847 were transformed into one year in the process of seven drafts and became Walden, or My Life in the Woods, not published till 1854. Even then the journey from journal to book was never quite complete. As Thoreau lay dying in 1862 he was revising proofs for a new edition of A Week and was writing Ticknor and Fields to suggest dropping the subtitle for Walden.

Howarth's exemplary study of Thoreau's "larger book" seems to me a very high form of literary criticism. Howarth climbs inside Thoreau's inkwell and tells us how and why he wrote, to what end, out of what fears and aspirations, and with what circuitous progress toward a "final" text. It would be hard to imagine a critic's account that more faithfully pursues the mystery of the writing process. The Book of Concord follows the chronology of Thoreau's written words and therefore travels the mountain range of the Journals, though it divagates into such non-journaled escapades as Thoreau's oration on John Brown, delivered in Concord; or his anti-slavery speech to be read on July 4, 1854, in Framingham, where William Lloyd Garrison burned a copy of the Constitution; or his profitable lecture engagements; or his work as a surveyor, which took him up and down New England and supplied most of his money. His books, however, sold only 2,300 copies during his lifetime, and he published only fitfully, and with dark and fully-justified suspicions of their editors, in magazines.

In addition to The Book of Concord, William Howarth, who teaches English at Princeton and has directed at least one new edition of Thoreau's writings, has admirably brought together Thoreau's expeditions, whether recounted in books or journals, into the mountains -- Katahdin, Monadnock, Kimeo, Greylock, Wachusett, Washington. In Thoreau in the Mountains these climbs are arranged by region. Howarth himself (sometimes accompanied by John McPhee) has retraced Thoreau's routes so as to verify Henry David's distances, identifications, and natural observations. He finds that Thoreau had a lot of trouble with certain birds and plants; that his capacity for "mensuration," as Emerson phrased it, had a wobble or two. He also, with scrupulous and elegantly designed cross-reference and 19th-century illustration, draws the difference in appearance between Thoreau's trails and wild places then and now. Many of them carry such names as "Thoreau Bog" and "Thoreau Spring." The mountaintops whither Thoreau repaired for his studies of mountain vegetation and natural history are now places whither people repair for their study of Thoreau.

A Conscious Stillness originated in the wish to revisit Thoreau's three major rivers, the Sudbury, the Assabet, and the Concord, mostly in a canoe, but the Concord River section was never written, owing to Edwin Way Teale's death. Alas, neither he nor his distinguished naturalist collaborator and illustrator Ann Zwinger has Thoreau's (or even Howarth's) capacity to relate the human and the natural. The tradition of the French moralists, as Howard Mumford Jones once pointed out, was never far from Thoreau's purpose, and his descriptions and characterizations of nature seldom fail to strike a concord with their human use or relevance. Teale and Zwinger, with somewhat myopic attention, give their eye and heart to the pickerel weed or the purple loosestrife without much attention either to man in general or Thoreau in particular. When Teale recounts the purple loosestrife's invasion of American soil in the 1960s and 1970s, he adverts to Darwin without noting that Thoreau read Darwin with rapt attention; and he refers to a modern book on the dispersal of seeds without apparent awareness that Thoreau spent his last years deeply engrossed in work on an unfinished book, "The Dispersion of Seeds."

Thoreau may take much credit for bugling the conservationist's creed, "In Wildness is the preservation of the world," but he saw no arbitrary division between the study of nature and of man: in the loneliest regions he came into conflict, into interaction, with people. The modern Thoreauvian is tempted to turn indifferently away from humanity and keep his eye upon the sparrow. Edwin Way Teale writes of one incident: "The canoe was aground on a submerged rock. Back-paddling, we extricated ourselves amicably. Thoreau's account of a similar situation, as related in A Week on the Concord and Merrimack Rivers, ends: 'So, each casting some blame on the other, we withdrew quickly to safer waters.' " And that has made all the difference.