Layered rocks on Mars...

Layered rocks on Mars...  The Curiosity rover recently sent back the photo at right (click to embiggen), showing clearly layered rocks.  These look to me like shale (or possibly slate, which is a metamorphic rock derived from shale), a rock typically formed at the bottom of bodies of still water, like lakes or lagoons.  I haven't seen any commentary on the Curiosity site about this yet, but if I'm right, it's even more evidence that Mars was once a watery body...