In January of 1969, British power blues quintet Fleetwood Mac came to Chess Records studios to jam with the likes of Willie Dixon, S.P. Leary, Honeyboy Edwards, and longtime Muddy Waters' pianist Otis Spann. The sessions were so rich and fruitful that three-fifths of the Mac (specifically bassist John McVie and guitarists Peter Green and Danny Kirwin) impressed Spann enough to cut a record with them at the same sessions. While the classic "Country Girl" and a seven-minute "Someday Soon Baby" (which features a lengthy intro from Green on which Spann can be heard barely off mic telling the rest of the band to "let him play on") ended up on the Mac's Blues Jam at Chess double set: remaining cuts included "Dig You" and "Walkin'" and are a near perfect match of Spann's exciting, emotive singing and the Mac's youthful muscle. The Biggest Thing Since Colossus was released on Mac manager/producer/strongman Mike Vernon's London-based Blue Horizon label.
AllMusic Review by John Duffy