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Raphael Pumpelly on secular rock disintegration

Raphael Pumpelly

Contents

About Raphael Pumpelly
Pumpelly's discussion of the role of secular disintegration in the
origin of rock basins
Pumpelly on the limited erosive power of continental glaciers
Conclusion
References & Bibliography
Related Sites

The Creation Concept | Controversy About the Glacial Theory

About Raphael Pumpelly

Raphael Pumpelly (1837-1923), American geologist, explorer, and
author, was born in Owego, NY. When he was seventeen, it was foretold
that he would "make long journeys by sea and through dangerous lands,
but that he would escape, unless taken unawares from behind by some
one of his companions."

In 1854 Pumpelly travelled to Europe with his mother, and he learned
French, German, and Italian. In 1856 he attended the Royal Mining
Academy at Freiburg, upon the advice of Emil Noeggerath, who
encouraged his interest in geology.

Pumpelly was employed as a mining engineer in Arizona in 1860. This
was a perilous time. In 1861 he travelled to California, and was
commissioned by the imperial Japanese government to make official
surveys in Japan (1861-63) of Yezo (later Hokkaido), exploring for
minerals. He surveyed the coal fields of China (1864) and made the
first extensive survey (1865) of the Gobi. He journeyed across Siberia
by sleigh. Later, he related these adventures in his book "Across
America and Asia".

Pumpelly found evidence that central Asia had once been occupied by
vast inland seas or lakes, which had slowly diminished in size,
leaving behind the Aral Sea and numerous small lakes. Their shorelines
were still visible. In his account of his journey across the Gobi
desert, he wrote [Ibid., p. 381]:

At no very remote geological time this region was the bed of an
extensive sea, which during one period of its existance formed part
of an ocean, extending over much of Siberia, Tartary, western Asia,
and eastern Europe, connecting the Polar sea with the waters of the
Caspian and Mediterranean. The elevation of the plateau was,
perhaps, the first step in the series of natural causes by which
the area of this great body of water was gradually diminished till
it was replaced by dry land.

He initially interpreted the extensive mantle of loess in China as the
deposit from a series of great lakes, which had disappeared. The
thickness of the loess in China exceeds 500 feet in some locations.

Pumpelly later accepted the theory proposed in 1877 by F. von
Richthofen that the loess of China and Central Asia had been
distributed by winds rather than water, but he noted: "The one weak
point of Richthofen's theory is the evident inadequacy of the current
disintegration as a source of material." [Pumpelly 1879 p. 135]

Pumpelly was appointed professor of mining at Harvard (1866-75), but
he was more interested in his researches on the iron and copper
deposits in the region around Lake Superior, for which he used
microscopes and thin sections for petrographic study. His major report
was published in 1873.

Pumpelly sensed the increasing importance of steel, and advised
investors to search for iron rather than gold. Some who followed his
advice made fortunes.

He was state geologist of Missouri in 1871. In 1884 he was in charge
of the New England section of the U.S. Geological Survey.

Pumpelly was in charge of the mineral industries survey for the 10th
U.S. census, and he served on the Northern Transcontinental Survey. He
conducted (1903-4) explorations in Turkestan, seeking traces of past
civilizations, financed by the Carnegie Institution. He wrote a number
of reports on his findings. In 1905 he was elected president of the
Geological Society of America.

Rollo Walter Brown, in his biographical essay "Cosmic Prospector", p.
200, gives this description:

He was tall of stature. Throughout his adult life he wore an
incomparable beard that reached well down to his waist-a "golden"
beard until it later became the gray beard of a patriarch. Though
his face expressed a dignified kindness, his eyes seemed always to
be looking far. He strode about with an easy self-forgetfulness, as
though he were at home in the universe. No one could escape feeling
that here was an extraordinary man. No one could escape feeling
that this man lived some sweeping career of extraordinary quality.

The mineral pumpellyite, a low temperature metamorphic mineral found
in the iron and copper ore region around Lake Superior was named after
him in 1925.

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Pumpelly's discussion of the role of secular disintegration in the origin of
rock basins

Pumpelly believed that the erosive power of ice sheets was not
sufficient to explain the fiords and lake basins formed in rock; he
proposed a mechanism of "secular disintegration" by which, over long
ages, continental rocks underwent deep decay, forming loose,
disintegrated material that was later easily eroded away by ice
sheets, forming lake basins. The disintegrated material, he thought,
was redeposited as drift by the ice sheets, or its fine fraction
transported and deposited as loess by winds. He wrote [Pumpelly 1879
p. 139-141]:

There are few problems in dynamical geology that have been
considered more difficult to solve than the origin of rock-basins.
Wherever my route between the great wall of China and the Siberian
frontier lay through regions of crystalline rocks, I found that one
of the characteristic features of the surface was the prevalence of
basin-shaped depressions of all sizes hollowed out of the rock. In
other words, if filled with water they would have been lakes
without outlets and with unbroken sides of rock. In some
exceptional instances it was clear that systems of intersecting
dykes had been less acted upon by the basin-making process than the
intervening rocks, and the basins were formed in these last.

The rock basins of Scotland have been graphically described by
Geikie, and while a great many of the countless lakes and lakelets
in the region of the crystalline rocks of North America and
Northern Europe are valleys of erosion with dams of glacial moraine
material, vast numbers of them undoubtedly fill rock-basins. An
ingenious explanation of the formation of these rock-bound
depressions given by Ramsay and accepted by Geikie as the only
reasonaable hypothesis, is that the rock-basins of the loch and
fiord kinds are due to unequal sculpturing by glaciers.

He says that where the bed of a glacier diminishes its angle of
slope, the vertical pressure of the ice on its bed becomes greater,
both owing to the lessened inclination and to the increased
thickness of the ice, while farther down the incline the widening
of the valley causes the ice to spread and consequently to diminish
its thickness and pressure; the result being a rock-basin dammed by
a rock-bar.

While this may be admitted, with some reservations, as a
satisfactory explanation for many fiords and lochs cut in the
declivities of a mountain range or of a steep coast, it is useless
in regard to the lake-basins of flat countries, like Finland and
British America. Geikie endeavours to use this hypothesis to
explain also the rock-basins observed by me in Central Asia; but it
is still more useless here as an explanation, because there are
absolutely no traces of glaciation in Central Asia, outside of the
high mountain chains. These Asiatic depressions are rough and
ragged, and the debris contained in them consists of ragged angular
fragments of the local rocks, while the glaciated basins of America
and Europe are smoothed and polished, and the debris they contain
consists of the rounded and scored material of the drift.

The basins of Asia were emptied by wind, and those of Northern
Europe and America were emptied by ice, but the wind and the ice
were only immediate agents employed in rapidly emptying basins
which had been long forming by a process common to both--the
secular decay of rock. I would thus seek the real cause, not in the
unequal nature and action of the instrument, but in the unequal
physical condition of the material operated on. It is evident, I
think, that we have in these residua an adequate source of material
for the glacial drift and for the loess, although other sources
have probably contributed in some regions to the formation of the
latter, as for instance, rivers which, fed by silt-loaded
glacier-streams, sink away on the plains of the central area,
leaving their suspended material to dry and drift on the surface.

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Pumpelly on the limited erosive power of continental glaciers

The following paragraph from the same paper [Pumpelly 1879 p. 141]
shows Pumpelly considered glacial action ineffective to explain the
extent of the distribution of drift material or its considerable
thickness in many areas.

In the warmly contested question as to the capacity of continental
glaciers in excavating solid rock, the great extent of "till" and
of the modified drift have been adduced as an evidence of this
power. It seems to me rather that the abundance of the drift
material may be equally well taken as in great part but not wholly
a measure of the effect of long-continued and undisturbed
disintegration and of the transporting power of ice, and that a
period of glaciation may be, as Rutimeyer insists, a period of
comparative rest as regards excavation of hard rock.

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Conclusion

Pumpelly's ideas about the evidence for a mechanism of in situ
disintegration of rock, to considerable depths, and the subsequent
erosion of unconsolidated material to excavate rock basins, to form
lakes, were soundly based. Pumpelly also correctly understood the
limited capacity of former ice sheets to break up the rocks beneath
them. His theory did not go far enough, however; his thinking about
the possible role of secular disintegration apparently was severely
constrained by uniformitarianism, and the glacial interpretation of
the drift championed by Louis Agassiz. But he can be credited with
conceiving and proposing an embryonic form of the disintegration
theory.

The drift can be interpreted without invoking ice ages; a
disintegration mechanism exists in the environment of rapid vertical
movements of the crust, accompanied by unloading as overburden was
removed. Erosion by currents generated as the flood waters flowed away
from centers of uplift, removed the disintegration product, promoting
disintegration by exposing fresh rock surfaces to decreased vertical
stress.

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References & Bibliography

* Brown, R.W. 1929. Cosmic Prospector, in: Lonely Americans,
Coward-McCann Inc., NY., pp 199-231.
* Champlin, Margaret Derby. 1994. Raphael Pumpelly : gentleman
geologist of the Gilded Age [Peggy Champlin]. Tuscaloosa :
University of Alabama Press.
* Pumpelly, Raphael, 1871. Across America and Asia. Leypoldt & Holt,
NY.
* Pumpelly, Raphael. 1879. The relation of secular rock
disintegration to Loess, Glacial Drift and Rock Basins. American
Journal of Science, 3rd series vol xvii, p. 133-144.
* Pumpelly, Raphael. 1891. The relation of secular
Rock-disintegration to certain transitional crystalline schists.
Bulletin of the Geological Society of America; p. 209-224.
* Pumpelly, Raphael. 1918. My Reminiscences. Henry Holt, New York.
* Willis, Bailey. 1925. Memorial of Raphael Pumpelly. Bulletin of
the Geological Society of America vol 36, 45-84.
* Dumas Malone, Ed., Dictionary of American Biography. Charles
Scribner's Sons, NY, 1935, Vol. XV, P. 264-6. (includes reference
to Pumpelly's and other pertinent publications);

RAPHAEL PUMPELLY (Sept. 8, 1837-Aug. 10, 1923), geologist,
explorer, mining engineer, was descended from Jean Pompilie, a
French Huguenot emigrant to Canada, through his son John who moved
to Massachusetts about 1700....
In 1881 under the patronage of Henry Villard, he undertook a
geological survey along the lines of a projected northwestern
railway, a work brought to an untimely end through Villard's
financial and nervous collapse.... [Pumpelly was] called one of the
most fascinating figures in American geology.

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Related Sites

Michigan's State Gem - "Isle Royale Greenstone"
About pumpellyite
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Copyright © 1997 by Douglas E. Cox
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The Creation Concept | Controversy About the Glacial Theory