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Dietz never stopped thinking about craters, whether on the Moon or on Earth.
This at a time when virtually every other geologist believed that there were no ter-
restrial impact craters and few if any on the Moon. Any candidates were damned
with the label “cryptovolcanic,” a term first applied in 1905 to the Steinheim Basin
in Germany, later established as an impact site. “Cryptovolcanic” encapsulated
Gilbert's illogical conclusion that although the origin of the structures was un-
known and although they showed no evidence of volcanism, nevertheless under-
ground volcanic gas explosions had created them.
In a paper presented at the Sixteenth International Geological Congress in 1933,
Walter Bucher had described his geological mapping of six cryptovolcanic struc-
tures in the United States, most of them in the Midwest or upper South. Following
Gilbert, he concluded that the structures “are the result of a sudden liberation of
pent-up volcanic gasses.” Bucher had noneed formultiple hypotheses: “All Amer-
ican cryptovolcanic structures represent special phases of the ascent of basic mag-
mas into the central plateau region.” 5
Most American geologists accepted Bucher's conclusion, but two professors at
Southern Methodist University, John Daniel Boon Sr. (1874-1952) and Claude C.
Albritton Jr. (1913-1988), disagreed. They became interested in impact cratering
in the 1930s and wrote a series of papers about the process, most of them pub-
lished in the journal of SMU's geology department: Field and Laboratory . 6 They
realized that long after erosion had removed the craters on the surface, the rocks
below would still retain the telltale evidence of impact:
We know that in addition to creating ephemeral depressions, meteorites deform surficial rock
layers when they strike the earth. Rim rocks of meteorite craters dip radially outward. Meteor-
ite impacts are, therefore, capable of producing geologic structures, and long after superficial
evidence of the impacts has been destroyed, these structures may be preserved. 7
Flatly refuting Bucher, Boon and Albritton wrote: “Certainly it can no longer be
maintained that all explosion structures are necessarily volcanic.” 8
Situated in the midst of the Illinois cornfields near the town of Kentland, about
as “lonesome” a site as one could find, lay one of Bucher's cryptovolcanic struc-
tures. 9 Robert Dietz knew of it from his days as a student at the University of
Illinois. In his autobiographical memoir, Dietz told how he came to visit the Kent-
land structure:
Flying long navigation training missions caused me to reflect about the Earth below in a gen-
eralized way. It is a form of remote sensing not unlike contemplating the Moon. One day in
1943, it occurred to me that the disrupted nest of lower Paleozoic strata in the Kentland quarry
in Indiana might not be cryptovolcanic as commonly supposed but an asteroidal impact scar.
Could not the orientation of shatter cones exposed there resolve this uncertainty? To test this
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