Geoscience Reference
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up a slingshot apparatus to fire clay pellets, and even using a large-bore musket
ing crater was indeed elliptical. Only when the angle was close to 90 degrees was
the pit circular. This led Gilbert to the idea that, analogous to his “plums in an as-
tral pudding,” the crater-forming meteorites had dropped vertically from a ring of
debris surrounding the Moon. But how had the ring gotten there?
Presaging the Chamberlin-Moulton hypothesis that would arrive a decade later,
Gilbert postulated that early in the history of the solar system a cloud of small, sol-
id objects had surrounded the Earth and “gradually coalesced” to form the Moon.
“The lunar craters are the scars produced by the collision of those . . . moonlets
jects—his moonlets—had descended vertically, not at random angles, and there-
fore had created circular craters. While this idea was wrong in detail, it did fore-
shadow the modern theory of the Moon's origin.
Gilbert presented his conclusions about the Moon in 1892 in his retiring address
as president of the Philosophical Society of Washington. He titled his speech “The
the talk not mention Coon Mountain, his “Origin of Hypotheses” paper, published
three years later, did not mention the Moon. Even more curiously, in “The Moon's
Face” Gilbert embraced the presence of impact craters on Earth, writing that many
moonlets “must have collide[d] with the earth, and the traces of their collision, if
ever discovered, will tie together at a new point the chronologies of satellite and
planet” (291). But Coon Mountain was not to be one of those craters. Gilbert got
the origin of Coon Mountain wrong, and nearly everyone agreed with him. Using
