The scottish/valse is exactly what's on the tin. You dance the A section as a scottish (medium tempo, 4/4 dance), then you switch to a waltz for the B section. Then back to a scottish. Then waltz. Et deliriums cetera. The trick -- and it is tricky -- is that the ones of the scottish have to be the same distance apart as the ones of the waltz. So, the 1-2-3-4 of the scottish has to fill the same amount of time as the 1-2-3 of the waltz. Got it?
"Le Cotillon Vert" is a bedeviling ear-worm of a tune. A bog norm standard that I found in Sylvain Piron's tradfrance. Here's the sheet music:
(UPDATE: And here is a link to diatojo's tab of the tune.)
And here is Sylvain's recording, a bit scratchy, maybe, played on his Castagnari Giordy:
Sylvain Piron, "Le Cotillon Vert"
You can hear that it's a bedeviling ear-worm of a tune! A few weeks ago I was listening to cabrette player Dominique Paris, and heard the same tune, though under the title, "Dis-moi Donc Suzon." Here it is as part of a set of scottish/valses.
Dominique Paris, "Dis-moi Donc Suzon - Pendant la Messe (scottishs-valses)"