Two vintage tape reels recorded in 1974 by Led Zeppelin are going to auction next month. And the majestic music contained on them supplied the foundations of the band's epic two-record 1975 set 'Physical Graffiti.'

RR Auction has the specifics: 10-inch tape reel, recorded on Ampex 406 quarter-inch tape, blah, blah, blah. But the juicy stuff is what's on those tapes -- unreleased studio mixes from 'Physical Graffiti,' including an early, eight-minute version of the classic 'Kashmir.'

You can listen to about a minute of the tapes in the above sampler that was thrown together to drum up interest in the auction, which runs from March 13-March 20. The starting bid on each tape is $300.

But here's what you get for all that cash: 'In My Time of Dying,' 'Sick Again,' 'Ten Years Gone' and a song called 'Désiré' that was later retitled for the album as 'The Wanton Song' on one tape; 'Trampled Underfoot,' 'Driving to Kashmir,' 'Custard Pie,' 'In the Light (Everyone Makes It Then),' 'Swan Song -- Part 1' and 'Swan Song -- Part 2' on another.

RR Auction says that the tapes "represent some of the earliest ever 'Physical Graffiti' recordings -- these unmastered examples served as starting points for the final songs, with bits and pieces retained while other parts were re-recorded."

Of course, there have been countless bootlegs available over the years chronicling the sessions for one of Zeppelin's greatest albums. You can even listen to one of the LP's outtakes here:

But this is an opportunity to actually own one of the tapes that probably hasn't been touched in almost 40 years. It comes from audio engineer Ron Nevison, who reconstructed a trailer as a mobile studio owned by former Faces member Ronnie Lane. Nevison is also auctioning less majestic music by Bad Company, who were on Led Zeppelin's record label at the time.