Creative Speculation

... is any mention of pumice, so let's add that to the list of reasons I've already given you. I have already acknowledged that it appears the composition of the concrete was not documented, but a specification of pumice would have been documented since it's more expensive and uncommon on the East Coast.

While it's true that absence of evidence is not evidence of absence of pumice in the mix, let's review for a moment where the burden of proof really lies here: If someone wants to argue that the iron spherules must be the result of thermite burning, as Jones & Co do, then by the principle of parsimony they are obliged to prove that they didn't come from more a more mundane source, and simply refusing to acknowledge that the concrete is the most likely source doesn't do the trick. Extraordinary claims, Occam's Razon, and all that.