That’s interesting. Hmm, I just looked it up too, and get this slightly varying description of the process; certainly the second def accords with some fierce stuff I’ve drunk in France!

marc
[MARK; MAHR]
1. A French term (known as pomace in English) for the residue (skins, pips, seeds, etc.) remaining after the juice has been pressed from the grapes.
2. A potent eau de vie distilled from this mixture. It's the French counterpart to grappa (the name used in Italy and California).

© Copyright Barron's Educational Services, Inc. 1995 based on THE FOOD LOVER'S COMPANION, 2nd edition, by Sharon Tyler Herbst.
http://eat.epicurious.com/dictionary/wine/index.ssf?DEF_ID=1867&ISWINE=T