A vertical furrow sounds more like what you would see on a pea comb, although some silkies have a sort of arched very shallow furrow. Can you post a photo? Some people are pickier on combs than others, and without seeing exactly what you mean, I wouldn't really be able to give decent advice.
There is a comb contest that has photos of various comb types. https://www.backyardchickens.com/t/644872/comb-contest-walnut and https://www.backyardchickens.com/t/644864/comb-contest-pea
I wish I could load photos. Since the change in the format, I can't seem to load any photos except on a rare occaision. I just tried to upload one, and after 46 minutes, it failed to load. This new format is not friendly to dial-up members at all. That all said, a Pea comb should have three rows of bumps? (forgive my lack of terminology here), this guy only has a split up the middle, where the normal Walnut comb split would be horizontial. I'll try to get my pic loaded to Photobucket and post a link.