I found this easily on Google, does nobody else look there?

"Like many old hymns, Amazing Grace, perhaps the most popular of them all, has a piecemeal history, and a not altogether clear one. Its words were written by John Newton and first appeared in the 1779 Olney Hymns book. But the author of the last of its seven stanzas, which begins with the words "When we've been there...," is unknown. The melody, popularly thought to be written by James Carrell, appeared in the volume Virginia Harmony (1831) and was used for the song New Britain. But some now attribute an earlier version of the tune to Charles Spilman and Benjamin Shaw, whose music anthology Columbian Harmony was published in 1829. To confuse matters a bit further, the words and tune first appeared together and in the form we know today in 1835, in Southern Harmony by William Walker."

Read more: http://www.answers.com/topic/amazing-grace-tune-new-britain#ixzz1r6s3uS2a