Fermentation goes on and on

Puzzling. Brewing an AG cascadian dark ale. OG was 1.070. Inoculated with American ale from a starter 9 days ago. Ferment temp @ 64F. CO2 production began promptly and after what I though would be the most vigorous period (the first three days) I exchanged the blow off tube for an air lock. 2 days later I noticed an awful lot of dried foam near the top and mouth of the carboy and the air lock chamber filled with Wort/yeast but no spill over. The foam had receded by the time I checked so I figured this was a one off. I replaced the airlock with a clean one. The next day the same thing happened. This time I replaced the air lock with the blow off tube and it looked like the ferment was settled down. I also checked the gravity (1.015) and tasted (Mmm Mmm good) That was about two days ago. This morning, there was evidence of wort in the blow off tube and lots of foam again and lots of CO2 production. Don't think I'm contaminated but I've never seen a ferment this active for such a long time. Your thoughts/observations appreciated.

What do you want to know. It's still fermenting. It was at 1.015, and may be going lower. You used a good healthy starter, so are more than likely getting a good healthy fermentation. I don't know what the worry is. Just because you haven't seen a fermentation that active before, doesn't mean there's anything wrong. Check gravity again in a couple of days.

Guess I'm looking for reassurance and reporting a new observation: fermentations may be wacky.