Is it "Cat's Cradle" or "Double X"?

It's both!  One of the interesting things about quilt blocks is the color placement.  It can turn one block into another.  Observe:

The quilt block on the left is "Cat's Cradle" (or Tennessee or Double Pyramid); the one on the right is "Double X (or Old Maid's Puzzle).  They're constructed exactly the same way, but the color inversion makes them different blocks.  This happens often--but it can be used to great effect.  I'll show you later this month what I mean....