I started the fermentation for a pale ale two and a half weeks ago, dry hopped it five days in and then racked it four days ago. The trub has fallen to the bottom and I just noticed a dark layer of liquid floating on the top. I've never seen this before. Does anyone have an idea of what it is?
I'm reasonably certain its beer ;) Even a pale ale looks dark in a carboy when it clears.
Your yeast is settling to the bottom and in that process the beer at the top is clearing. But this beer is having trouble clearing. That looks like a lot of sediment for a secondary on a pale ale, to me.
My recommendation would be to crash cool it. That will help drop everything out of suspension there, leaving you with bright beer you can rack off. Or just leave it be, I'm sure it will clear.