The Carters learned "The Cannonball" ("The Cannonball Blues") from African- American guitarist Lesley Riddle. Here's more info from my upcoming book:

"He was just gong to get old music, old songs, what had never been sung in sixty years," said Riddle. "He was going to get it, put a tune to it, and record it." Riddle also taught the Carter Family such songs he knew like "Coal Miner Blues," "The Cannon Ball," "I Know What It Means To Be Lonesome," and "Let the Church Roll On." Maybelle Carter learned to fingerpick and play slide guitar from Riddle. "You don't have to give Maybelle any lessons," said Riddle. "You let her see you playing something, she'll get it- you better believe it."

It was Riddle's job to learn the melody of the song. "If I could hear you sing, I could sing it too," said Riddle. "I was his tape recorder. He'd take me with him and he's get someone to sing the whole song. Then I'd get it and learn it to Sara and Maybelle."

Through Riddle and his friend gospel singer Pauline Gary from Kingsport the Carters also learned "On a Hill Lone and Gray," "I'm Working On A Building" and "On My Way To Cannan's Land." Through Riddle they adapted songs like Blind Lemon Jefferson's "See That My Grave Is Kept Clean" (See That My Grave Is Kept Green) and Blind Willie Davis' "Rock of Ages" (When the World's On Fire), which reportedly is the melody that Guthrie later used to write, "This Land Is Your Land." By 1937 Riddle had married and no longer worked with the Carter family. In 1942 he and his wife moved north to Rochester, N. Y. and lost touch the Carter Family.

Richie