In 1966 Bob Dylan was involved in a serious motorcycle accident and this led to an extended period of withdrawal - he did not tour again for seven years. However, this did not mean that he was musically inactive. In the summer of 1967 he began to record with The Band in the basement of a rented apartment near New York. Together, they wrote and recorded a large amount of material, working purely for their own entertainment without any intention of releasing an album.

The recordings are consequently loose, improvised, and generally less than serious in tone. However, the Basement Tapes - as they became known - quickly developed a cult status and were widely bootlegged. When finally in 1975 they were officially released, they reached the American top ten.

In Invisible Republic, Greil Marcus seeks to place the Basement Tapes in their historical context and also seeks to impose an enormous burden of meaning and significance on what many would regard as fairly inconsequential music: "The basement was an omphalos and the days spent within a point around which the American past and future slowly turned." He argues that the tapes as a whole evoke an "invisible republic", a self-sufficient imaginative world where "each performance makes part of a map".

Marcus, a highly respected music critic (author of Mystery Train), is a very erudite and also a very difficult writer. This book skips freely from Dylan's music to vast historical and sociological elaborations, and his style is self-consciously literary and freewheeling rather than being logical and critically detached.

At its best, the effect can be breathtaking. His lengthy analysis of the song Lo and Behold! (a short, humorous tune about which most people wouldn't think twice) is a masterful piece of writing, weaving in detailed reference to de Tocqueville, Melville's The Confidence Man, the 18th-century Puritan preacher Jonathan Edwards, and Martin Luther King.

In the space of about 10 pages one is given a panoramic view of American history, and after this build-up he is actually convincing when he claims that the throwaway first verse of Dylan's song "makes a story as shapely and complete as one of Hawthorne's Twice-Told Tales".

Marcus traces brilliantly Dylan's movement from folk to rock and dwells on the significance of his first electric performance, at Newport in 1965. He also analyses and exposes the ideologies that underlay the folk music revival of the Sixties, "music that seemed the product of no ego but of the inherent genius of all the people . . . It was the sound of another country - a country that, once glimpsed from afar, could be felt within oneself."

Unfortunately, Marcus starts losing his way in the later stages of the book. He attempts a comparative reading of The Basement Tapes and the famous Anthology of American Folk Music (compiled by Harry Smith), but it is all too long-winded and vague to be effective. Also, his ambitious approach to music analysis sometimes takes him too far and leads him to impose ridiculously elaborate interpretations on innocuous details.

Thus, a Doc Boggs banjo accompaniment contains "blue notes weighted down with a kind of nihilistic autonomy, a refusal to recognise any maker". Is that really what he hears, or is it what he would like to hear?

By the end of the book I was less than convinced by Marcus's attempt to establish The Basement Tapes as a vital part of American culture. However, his critical approach does open up new avenues of thought and shows at its best a rare historical awareness and sensitivity.

Tony Clayton-Lea is a freelance journalist and critic