Stamped Caution is science fiction story by Raymond Z. Gallun. Excerpt from the book: "It's a funny thing, but most monsters seem to be of the opinion that it's men who are the monsters. You know, they have a point. Ten minutes after the crackup, somebody phoned for the Army. That meant us. The black smoke of the fire, and the oily residues, which were later analyzed, proved the presence of a probable petroleum derivative. The oil was heavily tainted with radioactivity. Most likely it was fuel from the odd, conch-like reaction-motors, the exact principles of which died, as far as we were concerned, with the crash. The craft was mainly of aluminum, magnesium and a kind of stainless steel, proving that, confronted with problems similar to ones we had encountered, aliens might solve them in similar ways. From the crumpled-up wreckage which we dug out of that Missouri hillside, Klein even noticed a familiar method of making girders and braces lighter."