The Rock by Robert Doherty

height from the plain." The hand stabbed down and eighteen pairs of eyes followed. "There is no standing water in the bottom, but flat-lying sediments found there contain small shells, which indicates that a lake once filled the crater.
    "The earliest studies of the crater initially speculated that it was formed by either a volcano or an underground steam explosion. However, the discovery of some iron fragments lying very close to the surface soon challenged that theory. In November 1891 two members of the U.S. Coast and Geological Survey examined the area intensely. They speculated that because the crater is round, a meteorite must have struck at a nearly perpendicular angle.
    "They did a careful magnetic survey of the crater floor and discovered little evidence of buried metal. Using what I could best describe as the myopic-eyeball estimating technique, one of the men postulated that the amount of material on the rim would fill the crater completely." A snort indicated what the old woman thought of that. "Later, other more scientific studies clearly showed that the rim material is not sufficient to fill the crater.
    "In 1895 at the symposium of the Geological Society of Washington, the geologist Grove Karl Gilbert made a presentation on Coon Butte. He presented the various hypotheses and the evidence supporting each one, ranging from volcanic origin, to steam explosion, to meteor impact. His conclusion was that one could make no definitive conclusion based on the evidence, but that the crater most likely had been formed by a steam explosion."
    She was interrupted for the first time by a stocky figure sporting an Indiana Jones hat and a full beard. "Note how carefully Dr. Pencak describes Gilbert's presentation to the Geological Society. You will be required to read Gilbert's presentation before our next class meeting. It is a masterpiece of scientific inquiry."
    Dr. Susan Pencak continued without missing a beat. "Your professor is quite correct about the substance of Gilbert's address. Let us hope you read it more carefully than it was received in 1895. The common feeling by those listening to Gilbert was that he was definitively stating the crater was formed by a steam explosion. For over a quarter of a century the theory that Coon Butte was formed by a steam explosion stood with no challenge--blindly accepted by all."
    She turned and pointed behind her at the large boulders lying haphazardly on the rim. "It was not until many years later that the pattern of rock fragments scattered around the rim itself was examined. Large boulders, some weighing as much as five thousand tons, are found as far away as a mile from where I am standing. No steam explosion could have created that much force.
    "Massive amounts of pulverized rock known as silica are found both in the rim and in the crater. It takes tremendous pressure and heat to make silica out of solid rock. Additionally, fused quartz sandstone found in the crater indicates that a temperature at least as high as three thousand nine hundred degrees Fahrenheit occurred here at one time."
    Dr. Pencak paused and peered at the students, some of whom were diligently taking notes, others of whom seemed quite bored. She focused her single eye on a young man whose attention was wandering to the distant plain. "You there. Yes, you. Given all the evidence I have just presented and that which is laid out before your eyes, what do you think of the steam explosion theory?"
    The student blinked and spoke slowly as he tried sorting out the data, desperately wishing he had done the required reading for this road trip. "Well, Doctor, I suppose that might be an adequate theory, but I don't think a steam explosion could have fused quartz sandstone. Some sort of thermal effect or explosion had to have occurred to produce temperatures that high-much higher than could be caused by steam."
    "Ah!" she exclaimed. "A thermal explosion. Very good. Someone tell me what could cause such an explosion and