What are the oldest formations both offensive and defensive that are still in nfl playbooks?

I know the old T is not one of them. It's kind of too amateur in this day. But I am curious

I would have to guess the I formation or single back are pretty old. T formation is definitely the oldest.

@bgres077: yes but not used by nfl.

I would guess the Power I, or

That's not true. Chicago used it this very season.

They admitted after the game that they did it for tribute purposes, but the play they ran did gain 7 yards.

In playbooks though? I would say the power I.

The Powe I, I think