Published by the American Geological Institute
of the Earth Sciences
|A Natural History of the Sonoran
Desert, edited by Steven J. Phillips and Patricia Wentworth Comus,
University of California Press in collaboration with the Arizona-Sonora
Desert Museum Press. 1999. ISBN 0-520-21980-5.
Julio L. Betancourt
It was heartening to read a no-nonsense and comprehensive description of the natural history of the Sonoran Desert, my home turf for the last 22 years. In my travels across other deserts, I’ve always thought of the Sonoran as the most unique and diverse, from its varied geologic history and its 17 indigenous peoples to the many sources and kinds of storms that create its rain. Among other things, this Mexican-American desert hosts a phenomenal variety of plants, reptiles and pollinators unrivaled, not just by other deserts, but by rain forests worldwide.
The editors of this fine volume rely on an impressive pool of local talent to cover the balance of subjects, from geologic to human history, from arthropods and mammals, to reptiles and birds. Some of these talented folks work at the Arizona-Sonora Desert Museum, a wondrous labyrinth of mostly outdoor exhibits on the west flank of the Tucson Mountains. I would call Tom Van Devender, for instance, if I wondered when saguaro and palo verde first appeared in the fossil plant record of southern Arizona. Mark Dimmitt, who has a heavy hand in this volume, would be my first choice for queries about the flowering times and life histories of particular plants. And who better to talk about conservation biology or ethnobotany of the Sonoran Desert than Gary Nabhan. If my question involved how surface geology and soils affect local plant distribution, I would not hesitate to call Joe MacAuliffe of the Desert Botanical Garden in Phoenix. For pollination ecology, I would get an expert opinion from Steve Buchmann of the Carl Hayden Bee Lab, who reminds us that of the 5,000 species of bees in North America, more than 1,000 can be found within 30 miles of Tucson. And for a philosophical chat about late 19th century Tucson entrepreneurs like Leopoldo Carrillo, Sam Hughes and L. H. Manning and their landscape-altering shenanigans, I would go cross-town to my old buddy Tom Sheridan at the Arizona State Museum.
There is little missing in this book and much to recommend it. Of course, as with any multi-authored, natural history compendium, it contains occasional redundancies (desert pavement is explained in two different chapters) and some unevenness in presentation (the level of sophistication varies in the additional readings recommended after each chapter). Just the same, I’ve already recommended the book twice, first to introduce the Sonoran Desert to a newly hired professor, and again to a visiting sister-in-law.
This book was written to answer many questions, the kinds of questions that the annual half a million visitors to the Arizona-Sonora Desert Museum ask each year. In fact, this volume was the logical outgrowth of the Docent Handbook, a dog-eared compilation of natural history information that, for more than 50 years, has guided the training of the museum’s world-renowned volunteer interpreters. Naturally, then, this book showcases a trained ear for public interest and the trial-and-error experience of effective explanation to a broad audience. It offers tutorials on photosynthesis, monsoons and desert mirages, along with Nature-watching tips by month and locality.
It is also a graphic reminder of the natural wonders that will be lost if we pave the desert over and unconsciously whittle it down. More than half of the Sonoran Desert is no longer covered by native vegetation, dominated instead by 380 exotic plants. I live on Tucson’s north side, arguably one of the fastest growing metropolitan areas in the United States, wrapping itself around the scenic Catalina Mountains at an alarming pace. In the next 20 years, the Sonoran Desert in southern Arizona will be one of the great staging grounds for retiring baby boomers looking for a warm spot with a sunset view. Awareness raised by this book and other venues will determine whether or not these same baby boomers will witness pregnant bats from Mexico migrating north to feed on the nectar of night-blooming cacti in May.
Betancourt works in the Desert Laboratory of the U.S. Geological Survey and University of Arizona in Tucson.
|Understanding Mineral Deposits
by Kula C. Misra. Kluwer Academic Publishers (2000). 845 p.
ISBN 0-045530092. Illus. Cloth, $318.
Edward M. Ripley
The diverse geological settings of metallic ore deposits and the varied methods used in assessing their genesis make writing a comprehensive textbook on ore deposits a formidable challenge. Kula Misra has met that challenge and produced a first-rate book that reviews the techniques employed in ore deposit research and summarizes the geological and geochemical characteristics and origins of selected classes of metallic ore deposits. In a field that generates new data daily, Understanding Mineral Deposits is up-to-date and useful.
The book begins with a brief introduction that presents definitions of a few commonly used terms (e.g., orebody, tenor, reserve or resource) and reviews principles of ore formation and geochemical tools used to investigate and interpret processes of ore genesis. For example, the second chapter covers magmatic, sedimentary, metamorphic and hydrothermal processes of metal accumulation and ore formation, along with examples of modern or ancient deposits to illustrate the various processes involved in ore genesis. Chapters 3 and 4 deal with the application of mineralogical (mineral assemblages, phase relationships, hydrothermal alteration, paragenesis and zoning) and geochemical (fluid inclusions, trace elements, stable and radiogenic isotopes) data to the interpretation of mineral deposits. It also presents the basic theory underlying the analysis of fluid inclusions, stable isotopic fractionation, radioactive decay, element distribution and partitioning, phase equilibria, and textural analysis. The overview of the techniques used in critically evaluating the genesis of a mineral deposit is complete and focused and illustrates the steps a graduate student might logically follow in dissertation research. The 236 pages devoted to this section would be an essential component of an upper-level university course in metallic mineral deposits.
The second part of the book describes various types of ore deposits. Misra has done an excellent job of summarizing the wealth of literature that now exists for virtually all deposit types. He covers chromite, Ni-Cu sulfides, PGE, porphyry Cu-Mo-Sn, skarns, volcanic-associated massive sulfides (VMS), sediment-hosted massive Pb-Zn (SMS), sediment-hosted stratiform Cu (SSC), Mississippi Valley Type Pb-Zn (MVT), uranium, Precambrian iron formations, and gold. Although not all chapters are organized in exactly the same manner, the general scheme is to review the distribution and types of deposits within the overall class, present a series of examples of well-studied deposits, discuss the composition of the ores and their metallogenesis, summarize distinguishing characteristics and favored theories of origin, and give a short list of recommended readings. The discussions of the similarities and differences between deposit types, some that are often confused, are especially informative. For example, Misra discusses the distinctions between VMS, SMS, SSC and MVT deposits in a comparison following the MVT chapter. The chapters on uranium and banded iron formations include well-organized discussions on the development of Earth’s early atmosphere. An overview of the origin of gold in the conglomerates of the Witwatersrand Basin is included in the chapter on uranium. Readers should appreciate the detailed discussions of the possible origins for all of the deposit types and the vast amount of data upon which these evaluations are based.
Space limitations mean that some topics, particularly those covered in the first part of the book, cannot be treated in the detail that is often necessary for a thorough understanding of the principles involved. For example, accompanying text in advanced geochemistry would be required for a more complete treatment of all of the topics reviewed in chapters 2 through 4. Such a problem is inherent to most courses on ore genesis and to almost any economic geology textbook. Misra has at least provided the references that an interested reader would need for a more in-depth explanation of the foundations that underlie geochemical principles.
The length of the book reflects an increased knowledge base, and the likelihood that all of the information presented can be covered in a one-semester university course is small. Kula Misra states in the preface that a class in mineral deposits should be a capstone course that draws on concepts from several areas in geology. With this book he has succeeded in highlighting the multidimensional nature of economic geology. It is also an excellent reference for professional geologists and a useful text for a senior- or graduate-level course in metallic mineral deposits.
Ripley teaches in the Department of Geological Sciences at Indiana
|The Bonehunters’ Revenge: Dinosaurs,
Greed, and the Greatest Scientific Feud of the Gilded Age by David
Rains Wallace. Houghton Mifflin Co. (1999). 366 p. ISBN 0-395-85089-4.
Illus. Cloth, $25.
Stephen M. Rowland
Edward Drinker Cope (1840-1897) and O.C. Marsh (1831-1899) were the most prominent American paleontologists of the 19th century. Collectively, Cope, Marsh, and their hired collectors exhumed a staggering number of vertebrate fossils, mostly in the western United States. These were busy guys. Marsh published about 300 scientific papers on vertebrate fossils during his career, and he had as many as seven collecting parties in the field at one time. Cope published nearly 1,400 scientific papers in his career — 76 papers in 1880 alone, a rate of one paper every 4.8 days.
Despite some spectacular discoveries and their enormous contributions to paleontology, Cope and Marsh are best known today for sloppy taxonomy and anatomical blunders, and for feuding with each other. They were bitter rivals who often competed for the same fossil-rich deposits. Surrounding them are stories of spies and counterspies, stealing each others’ fossils and smashing bones in the outcrop to prevent the other guy from getting them. Wallace aptly refers to this style of field work as “smash-and-grab paleontology.” He includes a quote by paleontologist Bjorn Kurten that captures the ambivalence one feels for Cope and Marsh: They “transformed paleontology [into] a dynamic science and charged it with a spirit of discovery. At the same time, the rivalry and enmity between these two eminent scientists is a dark chapter in the history of paleontology.”
The Bonehunters’ Revenge is the first book-length treatment of the Cope-Marsh affair since Elizabeth Noble Shor’s 1974 book, The Fossil Feud between E.D. Cope and O.C. Marsh. The feud has lately become a hot topic: another Cope-Marsh book, The Gilded Dinosaur by Mark Jaffe, was published this year, and a biography of Cope, The Bone Sharp by J.P. Davidson, was published in 1997.
The Bonehunters’ Revenge is essentially a double scientific biography, alternately tracking the lives and careers of Cope and Marsh, emphasizing their interactions and influences on each other. It is a carefully researched, well-written account of a fascinating and disturbing episode in the history of American science.
Wallace is a writer-historian with no prior professional experience with paleontology or the history of geology, but he did his homework and fieldwork for this book. He spent time digging horse fossils with Greg McDonald at Hagerman Fossil Beds National Monument in Idaho, for example, and he explored the San Juan Basin (where Cope discovered the first-known Paleocene fauna) with Spencer Lucas of the New Mexico Museum of Natural History and Science. Endnotes and citations allow the interested reader to easily pursue selected topics in greater detail.
Wallace’s most significant contribution to the literature on the Cope-Marsh fossil feud is his insightful exploration of the role of the press. The book begins with a lengthy prologue about James Gordon Bennett Jr., owner and publisher of the New York Herald from 1868 to 1918. The Herald transformed the antagonistic relationship between Cope and Marsh from a private feud into a public spectacle. In January of 1890, Bennett’s newspaper published a splashy exposé of Marsh (the vertebrate paleontologist of the U.S. Geological Survey at the time) and John Wesley Powell (then the survey’s director). This article, written by a Cope confidant, was followed by multiple rounds of published responses and countercharges by Marsh and Powell, no-holds-barred attacks by Cope, and accusations and refutations by several other paleontologists who were sucked into the fracas. Wallace portrays Bennett as the cynical puppet master who manipulated the naïve scientists into airing their dirty laundry in public so that he could sell newspapers.
In general, Wallace deserves high marks. His book reveals the way in which North America’s vertebrate fossil record was discovered, how it contributed to the elucidation of the history of vertebrate groups generally, and how important the newspapers were in popularizing paleontology in the late 19th century. On the other hand, the complete absence of maps and the general paucity of illustrations were frustrating. I have not visited most of the fossil localities described in the book, and I wanted to get a better feeling for the rocks and fossils than the book provides. There are several photographs of people and a few period cartoons and sketches, but not nearly enough illustrations of fossils and strata to suit me. It’s a good story well told if not well illustrated.
Rowland teaches in the Department of Geosciences at the University
of Nevada, Las Vegas.
By Betty L. Gibbs and Stephen A. Krajewski
|Free Poster! A free contouring poster -- coming in the December print issue of Geotimes -- will contain more details on computer contouring using five common methods: Triangulation, Inverse Distance Weighting, Ordinary Kriging, Minimum Curvature and Trend Surface.|
Contouring: The construction of lines (contours) connecting points
of equal elevation on a map representing topography.
Glossary of Geology, fourth edition
For decades, geoscientists performed contouring of irregular spatial data by hand. Computer contouring started on mainframe computers in the 1950s but has become more widely used in the earth sciences since the advent of microcomputers in the early 1980s. Stand-alone contouring programs can be obtained from several public domain sources at no cost. Commercial programs range in price from $500 to tens of thousands of dollars, but enough inexpensive hardware and software is available that computer contouring is affordable for almost anyone.
Contours are a graphical display of spatial data relationships that help us to “see” where we cannot be. Whether the contours represent the top of a geologic formation or a quality value such as porosity or sulfur content, the contour lines are an interpretation of the data made by hand or with computer software. On the other hand, contours of surface topography show lines of equal elevation, closely approximate a surface and are definable from aerial photos or ground surveys. Contouring is also an art and the geologist uses available tools — whether the tool is a pencil or a computer — to produce a map that most accurately represents spatial data according to the expert’s experience, vision and perception. But even with computer contouring, uncertainty remains in knowing or proving that the contours truly represent the surface or values.
In general, making contour maps is easy. By hand, the process is slow and tedious but allows the easy addition of interpretations based on geological knowledge. Making contour maps with a computer is much faster, but the user has less direct control over how contours look than with hand contouring. Whether simple or sophisticated, gridding and contouring software is flexible enough to satisfy almost any contouring need with speed and convenience. Computer contouring is based on mathematical algorithms and is therefore not a perfect representation of data. It is necessary to constantly check results for errors and to make sure the contours are representative of the data. To produce the best possible contour maps, the geologist or engineer must know the software’s limitations and which contouring methods are most likely to produce an acceptable result. They must also be willing to experiment with different methods.
A person who does contouring by hand is usually confident in the interpretation and result. However, it has been proven many times that different people interpret a set of data in different ways — so what is a “correct” result? Surface contours are easy to check in the field. But contours representing an underground geologic formation’s structure or representing quality values are made by interpreting and estimating possible values between data points. Verifying such interpretations may prove impossible, costly or too destructive. The best defense against possible contouring errors is a clear understanding of contouring methods and their limitations, as well as a willingness to experiment, question results, and add reasonable interpretation when necessary.
A contour map constructed on a computer is too often considered a “true representation” of the actual surface with little or no error. How close the contouring method is to reality is rarely questioned. The mathematical world of the computer imposes a fixed interpretation on data derived from the random processes of Nature. Computerized contour maps should be examined and questioned and accepted only after many trials with different selections of control parameters.
Contouring errors (“noise” or artifacts) are introduced by selecting the wrong estimation method or algorithm or by incorrectly specifying the mathematical controls that dictate how the algorithm is applied to spatial data. Some contouring methods produce more artifacts than others, but most artifacts can be eliminated with proper selection of the control parameters. Recognizing potential errors in both manual and computer methods, and adjusting those methods when need be, is essential to produce a truly representative contour map.
Gibbs is president of Gibbs Associates in Boulder, Colo., and is a mining engineer with more than 30 years experience working for mining companies and as a consultant. E-mail: firstname.lastname@example.org
Krajewski, a geographer and geologist, is chief geologist for Industrial Ergonomics Inc. in Arvada, Colo., which provides training and consulting services. He also works with geographic information systems for the city of Loveland, Colo. E-mail: email@example.com
Active Tectonics and Alluvial Rivers by Stanley A. Schumm, Jean F. Dumont and John M. Holbrook. Cambridge University Press (2000). 276 p. ISBN 0-521-66110-2. Illus. Cloth, $80.
Comprehensive Dictionary of Earth Science: English-French, French-English, edited by M. Moureau and G. Brace. Editions Technip (2000). 1096 p. ISBN 2-7108-0749-1. Illus. Cloth, $160.
Evolution of the Cretaceous Ocean-Climate System, edited by Enriqueta Barrera and Claudia C. Johnson. Geological Society of America (2000). Special Paper 332. 445 p. ISBN 0-8137-2332-9. Illus. Paperback, $84.
Forced Folds and Fractures, edited by J.W. Cosgrove and M.S. Ameen. Geological Society of London (2000). Special Publication 169. 232 p. ISBN 1-86239-060-6. Illus. Cloth, $108.
Geodesy Beyond 2000: The Challenge of the First Decade, edited by Klaus-Peter Schwartz. Springer. (2000). International Association of Geodesy Symposia v. 121. 445 p. ISBN 3-540-67002-5. Illus. Cloth, $175.
Hiking Colorado’s Geology by Ralph Lee Hopkins and Lindy Birkel Hopkins. Mountaineers Books (2000). 238 p. ISBN 0-89886-708-8. Illus. Paperback, $16.95.
Holocene Land: Ocean Interaction and Environmental Change around the North Sea, edited by I. Shennan and J.E. Andrews. Geological Society of London (2000). Special Publication 166. 336 p. ISBN 1-86239-054-1. Illus. Cloth, $132.
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