structural geology, physiography, geophysics, and marine geology who wrote cogent syntheses that considered Earth from several vantages. In his earliest book, he presented what he called an “eclectic theory ” of volcanic action and magmatic differentiation, and thus I describe him as an “eclectic theoretician of the Earth.” The son of a tea merchant and a minister’s daughter, Daly was born on a farm near Napanee, southeastern Ontario, the youngest of four sons and five daughters. Late in his career, he recalled the simple life of a small town, the high standards of conduct expected by his parents, and an early introduction to the importance of hard work and wide reading. He was educated in public schools and attended Victoria College in Ontario (B.A., 1891; S.B., 1892; instructor in mathematics, 1892). There, inspired by Professor A.P. Coleman’s description of granite (“This is made of crystals.”), he decided on a career in geology. Encouraged by interviews with Nathaniel Southgate Shaler an

James H. Natland Rosenstiel

Reginald Aldworth Daly

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24  FEBRUARY 2006, GSA TODAY
Reginald Aldworth Daly 
(1871–1957): Eclectic 
Theoretician of the Earth
James H. Natland, Rosenstiel School of Marine and Atmospheric 
Science, University of Miami, Miami, Florida 33149, USA
Reginald Aldworth Daly was an authority in igneous petrol-
ogy, structural geology, physiography, geophysics, and marine 
geology who wrote cogent syntheses that considered Earth 
from several vantages. In his earliest book, he presented what 
he called an “eclectic theory” of volcanic action and magmatic 
differentiation, and thus I describe him as an “eclectic theoreti-
cian of the Earth.”
The son of a tea merchant and a minister’s daughter, Daly 
was born on a farm near Napanee, southeastern Ontario, the 
youngest of four sons and five daughters. Late in his career, he 
recalled the simple life of a small town, the high standards of 
conduct expected by his parents, and an early introduction to 
the importance of hard work and wide reading. He was edu-
cated in public schools and attended Victoria College in Ontario 
(B.A., 1891; S.B., 1892; instructor in mathematics, 1892). There, 
inspired by Professor A.P. Coleman’s description of granite 
(“This is made of crystals.”), he decided on a career in geology. 
Encouraged by interviews with Nathaniel Southgate Shaler and 
Josiah D. Whitney, Daly commenced graduate studies at Har-
vard under John E. Wolff, obtaining his Ph.D. in 1896.
Daly seemed always to absorb the better part of the knowl-
edge of his mentors and associates. Of the Harvard faculty, 
Wolff’s interests in ore mineralogy, petrography, and economic 
geology had the greatest influence on Daly at this time. Daly 
also was teaching assistant under Shaler and William Morris 
Davis, the latter attuning Daly to an understanding of physiog-
raphy and planation surfaces. At the same time, Daly formed 
important lifelong friendships with two contemporaries, crystal-
lographer Charles Palache and the future Hawaiian volcanolo-
gist, T.A. Jaggar. His closest friend, however, was Lionel Marks, 
soon to be a mechanical engineer in the physics department at 
Harvard, who introduced Daly to his future wife. These young 
men shared a community of mutually reinforcing interests that 
led them all to positions of leadership in their fields.
In 1893, Daly began his dissertation study of the geology and 
petrology of Ascutney Mountain, Vermont. The project culmi-
nated in the publication of a landmark paper (1903) that out-
lined his developing theory of the geological and petrological 
consequences of large-scale magmatic stoping and assimilation 
of roof rocks. The paper combined careful mapping, detailed 
petrographic descriptions, sophisticated treatment of chemical 
analyses of rocks, and analysis of the process of intrusion in 
light of contrasting densities of rocks and magma. The stoping 
hypothesis evidently came to Daly in a flash, while dropping 
off to sleep. Daly later wrote, “The solution then found still 
seems the best in sight, but its chief result has been the realiza-
tion that geology must be based on geophysics.”
Upon completing his degree, he obtained a superb post-
doctoral overseas fellowship in Europe (1896–1897), where he 
became an expert at thin section analysis under the petrog-
raphers Harry Rosenbusch (1836–1914) and Alfred Lacroix 
(1863–1948), toured many famous field localities, and attended 
the 7th International Geological Congress in Russia (1897). 
Looking at photographs taken at this time, Francis Birch (1958) 
described the young Daly as “physically impressive, sartorially 
elegant, [and] conspicuous among the somewhat worn-down 
gathering of international geologists.” 
In 1903, Daly married Louise Porter Haskell, who was from 
a distinguished Southern family, a graduate of Radcliffe Col-
lege, and the owner and headmistress of a girls’ school in Bos-
ton where she taught history and literature. Two of his books 
are dedicated to her as “inspiring fellow worker,” another as 
“comrade and wise counselor in the search for the meaning of 
things.” In a letter, she in turn described him as “a genius who 
remembers his mineral stage as few others ever have, & so 
feels earth-secrets as few others do.” After their marriage, she 
was his companion on journeys, field assistant, amanuensis, 
typist, manuscript critic, and editor. The Dalys had one child, 
a son named for his father and called Aldworth, who died of a 
fever from tubercular meningitis at the age of two. 
In 1901, Daly left Harvard, where he had been teaching 
physiography and oceanography. Despite the Ascutney work 
and the amenities of his position, he had not, as he later wrote, 
“made much progress in the development of original thought.” 
He joined the Canadian International Boundary Survey and 
undertook a monumental exploration of the Canadian–U.S. 
boundary from the Pacific coast through the wide belt of the 
Cascades and Rocky Mountains into the Great Plains. The sur-
vey was along the 49th parallel, the border between the United 
Reginald Aldworth Daly, from the Harvard archives.GSA TODAY, FEBRUARY 2006  25
States and Canada. Working with but one field assistant during 
five field seasons, Daly mapped a strip 5 to 10 miles wide and 
400 miles long through some of the most rugged country in 
North America. He then was able to present his fully devel-
oped theory in five chapters of his final report (1910, reprinted 
as Memoir 38 of the Geological Survey of Canada in 1912) and 
his first book, Igneous Rocks and Their Origin (1914). In 1907, 
he returned to academic life, first taking a position at Massa-
chusetts Institute of Technology, and then succeeding William 
Morris Davis as Sturgis-Hooper Professor at Harvard in 1912.
The maturity of Daly’s thought and the scope of his scholar-
ship are evident in the treatment of many topics in Igneous 
Rocks and Their Origin. Using Rosenbusch’s petrographic clas-
sification of igneous rocks, he divided 2631 chemical analyses 
to give average analyses of 116 petrographic types. He pre-
sented not only distributions of rock types of different compo-
sition, but described and classified the many forms of extrusive 
and intrusive rocks and the links between intrusive and extru-
sive bodies of igneous rock. The central problem of petrology 
at that time was to understand the diversity of igneous rocks. 
To Daly, crystallization differentiation by itself was insufficient, 
and he instead argued that magmatic stoping and assimilation 
contribute fundamentally to diversity. He also saw that beneath 
all igneous action, injection of basaltic magma into the crust 
was the essential precursor. Basalt is present in all associations, 
in all provinces, and at all times in Earth’s history. It is “the 
bringer of heat.” 
Drawing from geophysical conceptions of shells of the Earth, 
Daly proposed the existence of a universal basaltic substra-
tum beneath the crust that he argued was vitreous (a strongly 
viscous liquid; glass at high pressure) in its physical proper-
ties. Basalt was thus “primary” (a direct melt of the vitreous 
substratum). Gravitational accumulation of olivine then leads 
to formation of olivine gabbros seen as cumulates in so many 
intrusive bodies and the complementary olivine-free basalt so 
commonly found along the perimeter of the North Atlantic and 
in flood-basalt provinces. Ever since, discussion of basaltic pet-
rogenesis has had to deal with concepts of primary magma and 
the question of the potential uniformity of composition of its 
mantle sources.
Daly’s outer two shells of the Earth are a discontinuous layer 
of sediments and, beneath that, a silicic or acid crystalline 
layer, together comprising the upper part of the continental 
crust. He supposed that the acid shell is discontinuous beneath 
the oceans and viewed the continental crust as reworked by 
sediment melting, or syntexis, operating at and near basaltic 
intrusions. In this way, the crust becomes more strongly differ-
entiated toward granite than its average protolith, which Daly 
considered to be sedimentary material derived from ancestral 
basaltic and andesitic terranes. His theory required that the 
field relations be considered along with any theoretical or 
experimental inferences about the behavior of magmatic fluids. 
From his study of rock distributions, Daly was able to declare 
(1914, p. 52), “The igneous rocks of the globe chiefly belong 
to two types, granite and basalt … one of these dominant types 
is intrusive, and the other is extrusive. To declare the meaning 
of this fact is to go a long way toward outlining petrogenesis 
as a whole.”
Daly’s subsequent career added layers of expertise to his 
core concepts in petrology and field geology. In 1909, before 
completion of his Boundary Survey report, he traveled to 
Hawaii with T.A. Jaggar, accompanied also by Louise (this 
was shortly after their son’s death). There, the two scientists 
examined Kilauea volcano. The trip led directly to the estab-
lishment of the modern Hawaii Volcano Observatory, which 
Jaggar headed for nearly three decades. Daly’s first publication 
on Hawaiian volcanism was in 1911. His observations of island 
subsidence and reef distribution convinced him that fluctua-
tions in sea level were critical to the formation of the lagoons 
of barrier reefs and atolls. He published this as “The Glacial 
Control Theory of Modern Reefs,” also in 1911. After the First 
World War, he traveled extensively to study other volcanic 
islands (Ascension, St. Helena, American Samoa), ore bodies 
in Sweden, and (with Charles Palache) the Bushveld intrusion 
in South Africa.
His interests came to include uplifted beach rock, the bear-
ing of coral reefs on Pleistocene fluctuations in sea level, sub-
marine canyons, isostasy and glacial rebound, and the great 
questions of continental geology, including continental drift. 
He sparred with experimental petrologist N.L. Bowen in attrib-
uting the origin of alkaline magmas to the effects of limestone 
assimilation by basaltic magma rather than crystallization dif-
ferentiation (Daly, 1918). He endorsed continental drift in Our 
Mobile Earth (1926) and offered a mechanism for it: very low-
angle continental landslides or detachments slipping over a 
medium of extremely low strength, his own vitreous basaltic 
substratum, and compressing sediments in geosynclines. The 
idea is not far removed from today’s view of the geodynamics 
of accretionary prisms at subduction zones. In 1927, he favor-
ably reviewed the evidence for drift summarized by Alexander 
du Toit in The Geology of South Africa, which put him in a small 
minority of North American geoscientists who favored drift.
In 1930, together with physicist Percy Bridgman and other 
Harvard colleagues, Daly initiated an interdepartmental com-
mittee on geophysics, hiring Francis Birch, who held a Har-
vard degree in physics, to undertake experimental study of 
the properties of rocks at high pressure. An early graduate 
student in this program was Norman A. Haskell (not related 
to Louise), whose work on post-glacial Scandinavian uplift, 
Louise Porter Haskell, Daly’s 
“inspiring fellow worker,” 
Christmas 1901, a year 
before her engagement to 
Daly, from a family portrait. 
continued on p. 2626  FEBRUARY 2006, GSA TODAY
suggested by Daly, led to the first estimates of the viscosity of 
the upper mantle.
In 1933, Daly published a second edition of his 1914 book, 
this time calling it Igneous Rocks and the Depths of the Earth. In 
contrast to Bowen’s advocacy that crystallization differentiation 
led to granites, Daly continued to stress the importance of syn-
texis in the formation of continental crust, of superheat driving 
that syntexis, and of transport of alkalis in magmatic volatiles. 
Daly also added a full chapter on the physical properties of 
igneous rocks, which incorporated results of laboratory mea-
surements made in collaboration with Percy Bridgman.
In retirement, Daly presciently argued that the origin of the 
Moon involved collision of Earth with another planetoid (1946) 
and that the Vredevort structure in South Africa was produced 
by giant impact (1947). Daly became a U.S. citizen in 1920, 
was elected to the National Academy of Sciences in 1925, and 
received both the Penrose Medal of the Geological Society of 
America (1935) and the Bowie medal of the American Geo-
physical Union (1946). He published actively until 1952, and in 
1957 he wrote a biographical memoir of his Harvard friend and 
colleague, mineralogist Charles Palache.
Daly was a gifted lecturer who made good use of his and 
others’ drawings, diagrams, and photographs in both talks and 
published works. The title page of Our Mobile Earth, in which 
he endorsed continental drift, is wryly inscribed, following 
Galileo, “E pur si muove!” Daly’s forte was clearly in select-
ing among disparate observations and lines of reasoning and 
then reinforcing or extending hypotheses into new and more 
powerful syntheses. He tried to view geological processes from 
as many angles as possible. Almost all of us today are special-
ists, but to read Daly is to be reminded that ours is a multi-
disciplinary enterprise, and that understanding Earth requires 
mastery of many arts.
Daly died in 1957 at the age of 86; Louise, his wife, pre-
deceased him in 1947. Reginald, Louise, and Aldworth Daly 
are buried in the Haskell family plot at Elmwood Cemetery in 
Columbia, South Carolina.
ACKNOWLEDGMENTS
I’ve drawn on biographical information in Berkey (1936), Bill-
ings (1958), Birch (1960), Oreskes (1999), and Young (1998). 
I thank Angela Clark of the Rosenstiel School Library and the 
staff of the South Caroliniana Library at the University of South 
Carolina for assistance in gathering materials for this contribu-
tion. Warren Hamilton, Jerry Winterer, Paul Hoffman, Gerry 
Middleton, Robert Dott, and Bob Ginsburg provided helpful 
comments on the manuscript.
REFERENCES
Berkey, C.P., 1935, The award of the Penrose Medal to Professor Daly: Scientific 
Monthly, v. 42, p. 190–191.
Billings, M.P., 1958, Reginald Aldworth Daly, geologist [1871–1957]: Science, 
v. 127, p. 19–20.
Birch, F.A., 1960, Reginald Aldworth Daly, May 19, 1871–September 19, 1957, 
Biographical Memoirs: Washington, DC, National Academy of Sciences, 
p. 31–64.
Daly, R.A., 1912, Geology of the North American Cordillera at the 49th Parallel: 
Ottawa, Government Printing Office, Canada Department of Mines Geological 
Survey Memoir 38, 857 p., with a folio of maps.
Daly, R.A., 1914, Igneous rocks and their origin: New York, McGraw Hill, 563 p.
Daly, R.A., 1918, Genesis of the alkaline rocks: Journal of Geology, p. 97–134.
Daly, R.A., 1926, Our mobile Earth: New York, Scribners, 342 p.
Daly, R.A., 1927, Review of The Geology of South Africa, by Alexander L. du Toit: 
Journal of Geology, v. 35, p. 671–672.
Daly, R.A., 1933, Igneous rocks and the depths of the Earth: New York, McGraw Hill 
(Hafner Reprint, 1962), 598 p.
Oreskes, Naomi, 1999, The rejection of continental drift: Oxford, Oxford University 
Press, 420 p.
Young, D., 1998, N.L. Bowen and crystallization-differentiation: The evolution of a 
theory: Washington, Mineralogical Society of America, 276 p.
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(1871–1957): Eclectic Theoretician of the Earth

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(1871–1957): Eclectic Theoretician of the Earth

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