A century of science in America : $b with special reference to the American Journal of Science, 1818-1918
History
A century of science in America : $b with special reference to the American Journal of Science, 1818-1918
American journal of science; Science -- United States -- History
Granite, although regarded at this time as the extreme of the
metamorphic series and originating from sediments, was looked upon as
typically Archean in age, though in some cases younger. Such a doctrine
permitted such extreme misinterpretations as that of Clarence King and
S. F. Emmons on the nature of the intrusive granite of the Little
Cottonwood canyon in the Wahsatch Range. This body cuts across 30,000
feet of Paleozoic rocks and to the careful observer, as later admitted
by Emmons, shows clear evidence of its transgressive nature. But at that
time it was generally considered that granite mountains were capable of
resisting the erosion of all geological time. Consequently it did not
seem incredible to King and his associates that here a great granite
range of Archean origin had stood up through Paleozoic time until
gradual subsidence had permitted it to be buried beneath 30,000 feet of
sediments.[82]
It may seem to the present day reader that such a misinterpretation,
doing violence to fundamental geologic knowledge as now recognized, was
inexcusable; but in the light of the history of geology as here detailed
it is seen to have been the interpretation natural to that time. It is
true that a careful examination of the facts of that very field would
have proved the post-Paleozoic and intrusive nature of that great
granite body now known as the Little Cottonwood batholith, but Emmons
has explained the rapid and partial nature of the observations which
they were compelled to make in order to keep up to their schedule of
progress (=16=, 139, 1903).
Whitney had found some years earlier that the granites of the Sierra
Nevada were igneous rocks intrusive into the Triassic and Jurassic
strata. The Lake Superior geologists began to show in the eighties that
granite was there an intrusive igneous rock. R. D. Irving and Wadsworth
noted these relations. Lawson in 1887 pointed out emphatically (=33=,
473) that the granites of the Rainy Lake region, although basal, were
younger than the schists which lay above them. The granite gneisses he
held were of clearly the same igneous origin as the granites and neither
gave any field evidence of being fused and displaced sediments. From
this time forward the truly igneous nature of granite became
increasingly accepted until now the notion of its being made of
sedimentary rocks softened and recrystallized by the rise of the
isogeotherms through deep burial is as obsolete as the still older
doctrine of the Neptunists that granite was laid down as a crystalline
precipitate on the floor of the primitive ocean.
The recognition of the truly igneous nature of granites has been
followed in the present generation by a series of studies on their
structural relations and mode of genesis. A number of important initial
articles on various aspects of structure and contact relations have
appeared in the Journal, but this sketch of the history of the subject
may well stop with the introduction to this modern period.
Public-domain text, read in full here on John Shaqi.
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