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was not just that the rock types were the same; more convincingly, they
showed a similar stratigraphy.
Du Toit went far beyond Wegener in his understanding of Gondwana-
land; he was able to imagine both the early merging of the various continen-
tal pieces and their climactic melding into a single continental mass in late
Paleozoic time, followed by their fragmentation during the Mesozoic and
Cenozoic Eras. He became well versed in the stratigraphy not only of his
own continent but of the other members of Gondwana as well. Perhaps his
most telling argument supporting continental drift was his demonstration of
the remarkable similarity among late Paleozoic rock sequences on the vari-
ous continental pieces. On each he saw a basal unit of rocks deposited dur-
ing Ice Ages, known as glacial tillites, overlain by lake deposits containing a
small aquatic reptile named Mesosaurus and then by deltaic and river de-
posits; the units culminated in Mesozoic-aged basalt. Du Toit called this the
Gondwana System, known today as the Gondwana Sequence.
Wegener and du Toit turned out to be correct. But like Vincent van
Gogh, who never saw his genius acknowledged, neither Wegener nor du Toit
lived to see their great triumph of observation and reasoning confirmed. The
proof that continents wander did not burst into the scientific consciousness
until the early 1960s, when a slew of studies brought the theory of a static
earth tumbling down.
First, studies on rock magnetism showed that either the geomagnetic
pole had moved through time or the continents had. Both seemed utterly
impossible. But in short order, new evidence supporting continental drift
came to light. It was demonstrated that the mid-Atlantic ridge, a then
poorly known line of undersea mountains running down the middle of the
Atlantic Ocean, was composed of a chain of active volcanoes constantly in
the process of creating new oceanic floor. Next, a newly instituted program
of deep-sea drilling demonstrated that the age of the ocean floor increases as
one moves away from these submarine volcanic chains, which oceanogra-
phers began to call "spreading centers"; this discovery proved that the sea
floor was spreading and that, in many cases, it carried continents along for
the ride. But where was all this new ocean floor going? Seismic studies then
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