Memorial to Lincoln Dryden1903-1977

W. C. KRUMBEINDepartment o f Geological Sciences, Northwestern University, Evanston, Illinois 60201

Lincoln Dryden is best remembered by many of his friends and former students as an outstanding teacher. Except for a leave of absence during World War II, he served on the faculty of Bryn Mawr College from1930 until his retirement in 1970. His lectures, never dull, were spiced by amusing asides dropped casually here and there. This lightness of touch stemmed from Lincoln’s keen sense of fun and his refusal to take life or even himself too seriously. His informal approach and twinkling smile, occasionally slightly cynical, could be quite deceptive; his students learned rather quickly that a tightly disciplined mind lay behind his seemingly easy conversational style. This became apparent in his examinations, which required imagi­native integration of fact and theory, and hence proved to be much more than mere tests of memory.

Teaching undoubtedly was Lincoln’s main interest, inasmuch as he declined sev­eral higher-salaried nonacademic offers during his active career. As with most first-class teachers, Lincoln recognized the importance of original research as a foundation for ex­cellence in teaching. The same mental discipline that lay behind his lectures was clearly manifest in his research. One of his most important papers, widely acclaimed as a classic in the statistical analysis of heavy mineral data, was published in 1931, shortly after he earned his Ph.D. and before he attained his thirtieth birthday.

Lincoln was born in Baltimore in 1903. His family came from the Eastern Shore of Maryland, where his father, Abraham Lincoln Dryden, had served as a state senator. Lincoln was named directly after his father, but he later simplified his signature to its present form. He earned his B.A. and Ph.D. at Johns Hopkins, the latter degree sup­ported by a dissertation on the stratigraphy of the Calvert Cliffs near Port Republic on the western shore of Chesapeake Bay. These cliffs, famous for their fossil beds and rich in heavy mineral assemblages, were an enduring attraction to Lincoln even after retire­ment. He died in January 1977, in Calvert Hospital in Prince Frederick, virtually in sight of the bay and his favorite field localities.

In the 1920s Lincoln became interested in stratigraphic correlation by heavy mineral zones, and he saw the need for a more quantitative approach than was common at the time. Mineral frequencies were expressed as “ rare, common, abundant,” and so forth, or as ordinal numbers, though some workers made actual grain counts. Lincoln ad­dressed the problem in his 1931 National Academy paper, pointing out that arbitrary scales merely ranked the frequencies and were not amenable to ordinary algebraic operations. Moreover, neither the rankings nor the actual counts gave specific informa­tion on the accuracy of the estimates.

Lincoln was the first geologist to clearly show that evaluating the accuracy of heavy mineral counts is a problem in sampling error. He used the standard equation for

2 THE GEOLOGICA L SOCIETY O F AM ERICA

probable error, which for a mineral species having a given frequency, varies as the square root of the number of grains counted. His paper included a graph that plotted the percent of error against the number of grains counted for minerals ranging from 5 to 50 percent of the heavy mineral suite. The hyperbolic curves show that errors of 1 percent or less would normally require counting thousands of grains. Lincoln’s sugges­tion that a count of about 300 grains is adequate in most instances, with an error of only about 5 to 10 percent, has been generally accepted.

In 1935 Lincoln published a second important paper on the statistical treatment of heavy mineral data, and it proved to be far ahead of its time. The problem was to develop a measure of similarity between pairs of samples by comparing the kinds and amounts of heavy minerals contained in each. For this purpose he chose the square of the product-moment coefficient of correlation, r2, but its computation involved a “ transpose” of conventional methods. That is, instead of computing r for a given pair of minerals in a set of n samples, Lincoln computed r for a given pair of samples each having k heavy mineral species.

This seemingly radical departure from conventional practice was attacked on the grounds that the appropriate measure involved a Chi-square test not applicable to per­centage data. What was not realized at the time was that Lincoln’s procedure antici­pated the preliminary stages of Q-mode factor analysis, which did not enter geology until the early 1960s. In fact, Table 5 of Lincoln’s 1935 paper on the comparison of heavy mineral suites includes a data matrix with 8 rows representing a vertical set of Miocene samples and 9 columns listing their mineral components. The matrix is in proper form for modern R-mode and Q-mode factor analysis, the former for relations among the minerals and the latter for similarities between the samples.

Although Lincoln’s proposed method for comparing heavy mineral suites was not widely adopted, it nevertheless was a straw in the wind pointing to the ultimate need for a multivariate approach to the analysis of geological data. This need could not reasonably be met until the digital computer became generally available in the late 1950s, but the paper illustrates Lincoln’s foresight in anticipating this need at least two decades sooner than most of his contemporaries.

In 1933 Lincoln was married to Clarissa Compton of New York. Clarissa graduated from Bryn Mawr in 1932 with honors in archaeology and later earned her M.A. in the same subject. Clarissa audited Lincoln’s courses, learned to identify heavy minerals, and subsequently collaborated as junior author in his heavy mineral papers. Their first two collaborations, in 1938 and 1940, pointed out the stratigraphic importance of heavy minerals in the Philadelphia area and furnished a key to the common non-opaque species in eastern Pennsylvania. Their most important contribution was the 1946 study of rates of weathering of common heavy minerals in soil profiles, still cited thirty years later as an important contribution to our knowledge of mineral stability. A less well known though detailed collaborative report on source-rock heavy minerals of Pennsylvania was issued as a soft-cover publication by Bryn Mawr in 1960. Even when not cited as co­author, Clarissa worked with Lincoln both in the field and laboratory.

Although heavy-mineral studies were Lincoln’s major research subject, he was keenly interested in historical geology as revealed by areal geologic mapping. His work in Charles County, Maryland, some in collaboration with R. M. Overbeck, is an example. His course in historical geology at Bryn Mawr College was one of his favorites, and his 1959 paper on teaching this suoject displays the combination of dry humor and mild cynicism that characterized Lincoln’s conversational style.

M EM O RIAL TO LINCOLN D RY D EN 3

Shortly after Pearl Harbor, Lincoln gave a special course in naval communications to a selected group of Bryn Mawr undergraduates, many of whom became WAVE offi­cers in the Naval Communications Annex in Washington. Lincoln took war leave, and he and Clarissa also moved to Washington as civilian specialists to the Navy. Clarissa remained at the Naval Annex in highly confidential work for the duration; Lincoln was attracted to the Military Geology Unit of the U.S. Geological Survey. At his own re­quest he was later transferred on loan to the Beach Erosion Board of the Corps of En­gineers, which was engaged in landing-beach intelligence. After a period of briefing and preparation of a classified report on coral reefs, Lincoln moved with a small civilian group to the Pacific Theater as advisors to MacArthur’s headquarters staff on geolo­gic matters. As beach specialist, Lincoln became directly involved in the planning of landing operations. He followed with the landing forces, starting at Brisbane and moving to New Guinea and Leyte. After a year overseas, during which he survived a jeep accident in Hollandia and Japanese dive-bombing on Moratai, Lincoln returned to the Military Geology Unit in Washington with a War Department Citation for his efforts in the Pacific Theater.

At war’s end Lincoln and Clarissa returned to Bryn Mawr despite several tempting nonacademic offers. Life resumed its normal peacetime course—Lincoln worked with R. M. Overbeck on the geology of Charles County, Maryland, and in the early 1950s he and Clarissa traveled up and down the eastern seaboard with a portable laboratory searching for strategic minerals. Lincoln’s 1958 report on monazite resulted from this study.

The Calvert Cliffs of southern Maryland, which Lincoln first studied in connection with his doctoral dissertation, became his favorite field locality. It was there he de­veloped his continuing interest in the fossil fauna of the Atlantic coastal plain. In his opinion this thirty-five mile stretch of cliffs could not be matched in richness of fossil content by more than half a dozen sites in the world. He himself found a fossil skull partially exposed, which when exhumed with expert help led to the complete skeleton of a Miocene whale, now a possession of the Smithsonian Institution.

In the late 1960s Lincoln was Director of Scientific Studies at the site of the Calvert Cliffs Nuclear Power Plant. This project, manned by personnel from the Smithsonian Institution and the U.S. Geological Survey, was conducted under the auspices of the Maryland Academy of Science. The study emphasized the paleoecology of fossil com­munities that came to light as excavations at the plant site were carried on. After Lincoln’s retirement in 1970 the continuing appeal of the Calvert Cliffs led Lincoln and Clarissa to purchase a house at Scientists’ Cliffs near Port Republic, Maryland. From this vantage point Chesapeake Bay spread out as a panorama and the rich fossil beds lay almost directly below. It was Lincoln’s last home.

Lincoln was a Fellow of the Geological Society of America, an active member of the American Association of Petroleum Geologists, and a member of the National Association of Geology Teachers. His major devotion to teaching and his outstanding ability to project his own enthusiasm to his students was long recognized on the campus at Bryn Mawr College. It was formalized by the college in May 1970, several months before Lincoln retired, by naming him recipient of the Christian R. and Mary F. Linback Award for Distinguished Teaching.

Lincoln’s reputation as a research scientist was assured by his early study of accu racy in heavy-mineral analysis and by his collaborative papers with Clarissa. He also earned another kind of distinction that few sedimentologists can claim. In addition to

4 TH E GEO LO G ICA L SOCIETY O F AM ERICA

the fossil whale already mentioned, Lincoln found a new species of fossil crab at Cal­vert Cliffs. It was named Necronectes drydeni Rathbun in recognition of his continuing interest in Atlantic coastal plain fossils and by his thoughtfulness in collecting speci­mens for his paleontological friends.

SELECTED BIBLIOGRAPHY OF LINCOLN DRYDEN(M o st b ib liograph ies lis t D ry den as A b ra h a m L in c o ln D ry den , Jr.)

1931 Calvert (Miocene) tilting of the Maryland Coastal Plain: Washington Acad. Sci. Jour., v. 21, p. 131-134.

----- Accuracy in percentage representation of heavy mineral frequencies: Natl. Acad.Sci. Proc., v. 17, p. 233-238.

----- Glauconite in fossil foraminiferal shells: Science, v. 74, p. 17.1932 Faults and joints in the Coastal Plain of Maryland: Washington Acad. Sci. Jour.,

v. 22, p. 469-472.----- Heavy minerals of the Coastal Plain of Maryland: Am. Mineralogist, v. 17,

p. 518-521.1933 Xenohelix ’m the Maryland Miocene: Natl. Acad. Sci. Proc., v. 19, p. 139-143.1934 Cumulative curves and histograms: Am. Jour. Sci., v. 27, p. 146-147.1935 A statistical method for the comparison of heavy-mineral suites: Am. Jour. Sci.,

v. 29, p. 393-408.----- Structure of the Coastal Plain of southern Maryland: Am. Jour. Sci., v. 30,

p. 321-342.1936 The Calvert formation in southern Maryland: Pennsylvania Acad. Sci. Proc.,

v. 10, p. 42-51.1938 (and Dryden, Clarissa) Stratigraphic importance of heavy mineral studies in the

Philadelphia region: Pennsylvania Acad. Sci. Proc., v. 12, p. 97-103.1940 (and Dryden, Clarissa) A key to common non-opaque heavy minerals of the

eastern Pennsylvania region: Pennsylvania Acad. Sci. Proc., v. 14, p. 49-54.1941 (and Dryden, Clarissa) A note on hyacinth zircon in the rocks of the Honeybrooke

upland (Pennsylvania): Pennsylvania Acad. Sci. Proc., v. 15, p. 73-75.1945 The Military Geology Unit (U.S. Geol. Survey): Econ. Geology, v. 40, p. 589.1946 (and Dryden, Clarissa) Comparative rates of weathering of some common heavy

minerals: Jour. Sed. Petrology, v. 16, p. 91-96.1948 (and Overbeck, R. M.) Geology of Charles County (Maryland): Maryland Dept.

Geology, Mines and Water Resources, Charles County, Rept. 13, p. 6-17.----- Popular account of the geology of Charles County (Maryland): Maryland Dept.

Geology, Mines and Water Resources, Charles County, Rept. 13, p. 18-28.----- (and Overbeck, R. M.) Detailed geology (Charles County, Maryland): Maryland

Dept. Geology, Mines and Water Resources, Charles County, Rept. 13, p. 29-127.----- Mineral resources of Charles County (Maryland): Maryland Dept. Geology,

Mines and Water Resources, Charles County, Rept. 13, p. 128-129.1958 Monazite in part of the southern Atlantic Coastal Plain: U.S. Geol. Survey Bull.

1042-L, p. 393-429.1959 On teaching historical geology: Jour. Geol. Education, v. 7, p. 67-70.1964 (and Dryden, Clarissa) Source-rock heavy minerals of the Pennsylvania Area:

privately printed at Bryn Mawr College, 55 p.

Printed in U.S.A. 6 /78