Is that really "white stuff" in both trenches or is its appearance a product of the reflective qualities of mashed down Mars "soil?"

If it is "white stuff" at the Spirit site, and it is so close to the surface, doesn't that affect the notion that the whole surface of Gusev is volcanic? If the "white" material is just barely below the surface, as it appears to be (understanding that our eyes may be deceiving us) and if the material on top is only a few centimeters deep, then the hypothesis of a purely volcanic Gusev surface may become inoperative.

Of course we still don't know the origins of the white stuff, nor is its composition clearly understood. (Sulfur? Sulfate? Sulfide? Sulfamine? Sulfa? ;-)) And in this case, we can't even be sure it is there.

But if it is....

Meanwhile, it looked like some of the Spirit images showed spherules on the Gusev surface. If so, what is their origin, and how might it compare to the origins of the Opportunity site spherules? (If "white" material underlies the Gusev site, are spherules found embedded within it?)

Constant amazement.

Cheers, BRFelix