5 December 2022
Mafic blocks in Wind River Range granite
Got these photos from a reader, showing outcrops in the northern Wind River range (ESE of Island Lake). The question, inevitably, is are these MMEs (microgranular mafic enclaves) or xenoliths?
They’re fine grained and mafic… but some lithologies of xenolith could be too!
This next set shows what appear to be a bunch of blocks strung out in a line…
This one is shaped like a toaster or a television set:
Note that more pronounced weathering of the mafic blocks, and also how the granite’s fabric wraps around it on at least three sides.
Any thoughts, igneous petrologists?
2 December 2022
Friday fold: Hidden Rock Park, Goochland County
Two weeks ago was the annual Virginia Geological Field Conference, which was centered this year on the Goochland Terrane, an interesting block of crust in the Piedmont which shows some similarities to the Blue Ridge geologic province, but also shows some differences that suggest it’s not just a mini-Blue-Ridge. One of the best exposures was in Hidden Rock Park, where a series of “whaleback” outcrops expose things like this:
There, a granite dike cuts through a gneiss, and then that granite dike is folded and boudinaged. Annotated:
Happy Friday!
1 December 2022
Mask of the Sun, by John Dvorak
Inspired by How The Mountains Grew, I ordered the rest of John Dvorak’s oeuvre recently. I read the first over Thanksgiving break – a great nonfiction look at eclipses. The basics of lunar and solar eclipses are dispensed with early on, and Dvorak then spends his time on understanding of eclipses in antiquity, the gradual accumulation of insight into the causes and timing of eclipses – thus permitting them to be forecast, and how this understanding came part and parcel with newfound scientific insights about the nature of the solar system in general. The influence of eclipses on history and literature is explored next, and the many tales of adventurous travel to go to a place where eclipse observations are to be made, sometimes successfully and just as often ending in failure due to an inopportune cloudy sky. Emily Dickinson, Albert Einstein, and Christopher Columbus all make appearances, but the most attention is given to the astronomers who made key advances in advancing humanity’s understanding of this amazing phenomenon, and how they cleverly answered questions such as whether there is a planet inside Mercury’s orbit, or what the nature of the corona might be. And because the phenomenon invariably triggers awe and wonder, a fair amount of attention is given to the experiential nature of eclipse viewing, as well as the phenomenology of those few minutes. (There is a particularly hilarious anecdote about Thomas Edison being besieged by chickens coming home to roost in the sudden darkness of a solar eclipse, messing up the experiment he has inadvertently set up in their coop.) Dvorak makes the point that our planet is pretty much unique in the eclipses it experiences. Further, this moment in time is pretty much perfect for solar eclipses, but in the future the Moon will slip further away from Earth, and thus won’t be able to completely “cap” the sun any more. There will be a “last eclipse” someday in the far future – so enjoy them while you can.
30 November 2022
Ichnoanalogue
Another glimpse of sand on the beach at Esterillos Oeste, Costa Rica…
This time, I offer you a trace of an organism moving through the wet sediment:
Note the two parallel lines of tracks laid down by little feet, and the central groove that overprints them. It reminded me very much of this similar arrangement, from near St. Andrews in Scotland, but: (1) this is the underside of a bed rather than its upper surface, and (2) it is of a rather more substantial magnitude…
28 November 2022
Getting ripped
I traveled to Costa Rica over the Thanksgiving holiday, and enjoyed exploring the coastal outcrops near Esterillos in Puntarenas province. Before I get to the rocks, though, I thought I’d share a bit of the patterns on the sand on the beach. These ripples, for instance:
They’re as large as pythons!
And in this set, large antidunes are bedecked in a smaller surficial “skin” of oscillation ripples:
I didn’t include a sense of scale in either of these ripple photos because I just found them so strikingly pretty, and didn’t want to mar the beauty by sticking any science in there.
At another location, at low tide, the land was seeping groundwater out through the beach, resulting in a neat ‘braided’ pattern made plain by the high contrast between biogenic particles and the volcaniclastic bulk of the sediment. Check it out – this view is looking “upstream” but I’m not sure there’s anything diagnostic here to show that for sure.
I love stuff like this; I spent a lot of quality time watching standing waves move upstream (antidunes migrating) and neat little mini-deltas forming and being eroded, endless adjustments of little bits of the Earth system under the influence of moving water.
27 November 2022
Book report
An Immense World, by Ed Yong
Pulitzer Prize winner Ed Yong’s second book has arrived, and it’s about animal senses. Early on, he introduces the concept of the Umwelt as a way of thinking about the totality of an individual organism’s sensory perceptions. You can smell, taste, hear, touch, and see, for instance, but you can’t sense ultraviolet light, or infrasound, or magnetic fields. Many other animals can – and so their Umwelten are different from yours. What is it like to be a bat? Yong explores this question further than Thomas Nagel was able to, and it’s a fascinating journey. Yong writes with confidence, empathy, and thoughtful consideration. He visits the laboratories and field sites of dozens of biologists who are probing the limits of animal senses, and comes into direct contact with diverse creatures – otters and star-nosed moles, moths and songbirds and octopuses — and bats. On the whole, the book is a very refreshing read, full of wonder and humor as well as sober appreciation for the perspectives of others. One thing I’ll note however in the way of criticism: about 1/10th of the book is footnotes! There are a tremendous number of tangential comments or quirky insights or tantalizing connections that don’t fit into the main sweep of the narrative, and Yong definitely invokes The Footnote as a tool for resolving that conundrum, over and over again!
The Catskill Delta, edited by Donald Woodrow and William Sevon
A Geological Society of America special “paper” (#201), this volume includes 17 papers (and one abstract without the paper!), all about various aspects of the middle- to upper-Devonian stratigraphy and paleontology of the Catskill clastic delta in the Appalachian Basin. I read it last weekend on the porch, enjoying delving into paper after paper about a common theme, all that sand and mud shed off the Acadian Orogen. This isn’t the typical sort of light reading I’d choose for a sunny Saturday afternoon, but a colleague who recently retired gifted me a box full of books and maps and posters, and there are some real gems in there amid the dust and dross. I’ve been thinking about the Acadian Orogeny more over the past year as I try to synthesize my geological experiences last summer in Maine with other regional data. I’m trying to put together a coherent “case study” on the Acadian for my free, online Historical Geology text”book,” and this volume stimulated my thinking about the clastic signature of that mountain-building event. Of particular interest were the black shales that are now the source of so much natural gas in places like western Pennsylvania.
The 1619 Project, edited by Nikole Hannah-Jones
A collection of essays (and even some short fiction and poetry) that reframes American history in light of the practice of chattel slavery. Starting in 1619 in Jamestown, British colonists (and later their political descendants, Americans) enslaved Africans, and that isn’t just an incidental historical act that can be swept under the rug because it makes modern Americans uncomfortable. Instead, Hannah-Jones and her coauthors argue, it is the central fact of American culture and governance, and at the very heart of our nation’s story. Despite the abolition of slavery, the cruelty and division it fostered are (forever??) baked into the American experience. This is a book that doesn’t flinch from that perspective, but explores it deeply and thoughtfully. The essays included explore politics, economics, capitalism, citizenship, and justice, all putting slavery front and center, where it makes sense in explaining myriad features of the modern American experience. The book argues that this is proper and necessary to really get how this country functions. American history didn’t start in 1776, Hannah-Jones and her co-authors assert, it started in 1619.
Some Assembly Required, by Neil Shubin
The author of the superlative Your Inner Fish (and the underwhelming sequel The Universe Within) returns with a third book. I loved it – it delves into evolutionary developmental biology (evo devo) and sources of evolutionary novelty (the grist for natural selection’s mill) that are distinct from mere point mutations. Jumping genes, endosymbioses, viruses inserting their code into the middle of our code, changes in embryo timing – it’s complicated. But the past several hundred years, and particularly the past 75, have led to astounding insights that show us how genes manifest in the building of bodies. Shubin does a great job profiling key scientists whose thoughtful observations and clever experiments revealed key mechanisms by which these mechanisms functioned outside the basic “central dogma” of modern evolutionary theory. The story is more complicated than we had supposed, but its complications are fascinating and insightful. Top notch science writing by Shubin. Highly recommended.
The Belt Series in Montana, by Clyde P. Ross
Another “paper” that’s really a book. This one is USGS “professional paper 346,” published in 1963. As with the previous volume, it’s one that I recently “inherited” from a colleague who retired. I find the Belt Supergroup fascinating and enticing, and I read this 112 page volume cover to cover. It maybe be more than half a century old, but the Belt is older! It holds up very well, and I found particularly fascinating the long and inconclusive discussion of whether the Belt represents “marine” or “lacustrine” deposition, as well as the extensive listing of Belt-age equivalents in other parts of the North American continent, and what light they can shed on the Belt. I found inspiration here in making deliberate visits to some of these Mesoproterozoic strata that I haven’t yet seen, and thinking about the different world in which they were laid down.
13 November 2022
A Geological Miscellany, by G.Y. Craig & E.J. Jones
A fun, if a little musty, compendium of random writings about geology and geologists from a wide variety of sources, excerpted and packed together into a slim paperback volume. It begins with Mark Twain and concludes with Russell Baker, and there are hundreds of entries in between – some poems, some short essays, some clipped correspondence, some newspaper articles, and so on. It’s miscellaneous, as the title suggests. Many of these are interesting from the perspective of illumination of past working conditions among geologists – persnickety government-issued instructions for maintaining a field camp in New Zealand, for instance, or formal letters telling the staff paleontologist that he’d better damned well show up for work. Others could be categorized as whimsy, some of it in the spirit of goofy inspiration during a dull moment, or the intentional letting-down-of-one’s-hair that accompanied boozy meetings of the Pick and Hammer Club. Several menus are included, of bygone feasts hosted by the Geological Society of London with roasted turtles and pigeons and turbots and eels and dozens of other options. The book is the sort of thing to keep on one’s bedside table as light reading before bed, a small bite at a time, nothing so meaty as a true “chapter.” But because of its heavy emphasis on the historical written record, stretching back to the founding of geology as a discipline in the stratified, sexist western Europe of yore, the people being discussed are even more starkly white and male than geology’s present-day lamentable lack of diversity. Because it carries this sense of “that’s what a geologist is,” I’m not sure I’d recommend it, but there are enough little gems of humor in here, separate from the identity of the humans that produced them, that I could see gleaning out a few of the most poignant quips for general consumption – I’m thinking a geo-poetry reading, or some such. Even William Smith contributed a funny little poem!
12 November 2022
Catastrophes and Lesser Calamities, by Tony Hallam
This is a thoughtful volume on mass extinctions written for the novice. One thing I really liked about this book is that it was written very clearly from the mind of a skeptical scientist who is conscientious about explaining each step in his thinking while explaining fairly complicated, murky stuff for a lay audience. Hallam succeeds magnificently in defining ideas first, and only later attaching jargon or terminology to the concept. I really liked the organization of the book, too – rather than the typical march through mass dying through time (i.e., a chronological approach), Hallam organizes his discussion around the various proposed causes of mass extinction, and explores each of those in depth, citing evidence from the Big Five and other events in Earth history that both support and weaken the causative hypotheses. Going at it this way puts a different emphasis on thinking about mass extinctions – it’s a mechanistic approach rather than a historical whodunnit. I learned a lot, and particularly appreciated Hallam’s review of the literature on the role of sea level change in driving mass extinction events – something that often gets left out of the discussion when more attention-grabbing topics like ocean anoxia, large igneous provinces and (yes) meteor impacts are also in the mix. All told, it’s a solid, readable book. The one odd note was a four or five page digression into adventure stories while collecting data in remote corners of the world. Hallam’s discussion of the Pleistocene megafauna extinction really influenced my thinking on that issue. This was not one of the “Big Five” but still of keen interest to many given its unusual scope (large terrestrial species) and timing (shortly after humans arrived on various landmasses).
11 November 2022
How the Mountains Grew, by John Dvorak
This enjoyable book offers “a new geological history of North America,” summarizing a vast swath of research from many disciplines to expound on the continent’s evolution over deep time. The geographic scope is a little inconsistent – it mainly centers on the Lower 48 United States, but includes bits of Canada and a brief foray into Mexico for the Chicxulub impact crater, but also mentions Hawaii (which though part of the U.S. isn’t part of the continent) while almost entirely ignoring Alaska. But for the areas it focuses on as relevant to telling the story of the continent, it delves into great, highly-specific detail: the kind of detail that appeals greatly to a geoscience outreach nut like me. Specific waterfalls in state parks, specific exit numbers to reach key outcrops, this glacier has retreated by that many miles, and so forth — all this is evidence of a willingness to luxuriate in the level of geographic detail that might put a novice off, but suggests to me that Dvorak really knows what he’s talking about. Then again, there were some errors that seemed preventable: placing India in the northern hemisphere at the time of the Deccan Traps’ eruption, mistakenly referring to the Coastal Plain as “the Piedmont,” indicating that Mt. Moran’s 800 Ma mafic dike was intruded “near the end of the Paleozoic.” Maybe these are pretty minor in the grand scheme of things – the book is PACKED with details, and it’s probably inevitable a few of them might not be exactly on target. I found much to appreciate in How The Mountains Grew: new fossils to check out, new parks to put on my “must visit” list, new perspectives on large scale teleconnections between disparate phenomena. I’d never heard of Dvorak’s writing prior to seeing this volume pop up in a “related books” algorithm on AbeBooks.com, and I’m so glad it did. Turns out he has three other titles, which I just ordered — and look forward to reporting on them to you here someday!
12 October 2022
Geopedia, by Marcia Bjornerud
My favorite popularizer of modern geology is Marcia Bjornerud. Her sensibility for what is interesting and important matches very nicely with my own – I feel she is a kindred spirit, though one infinitely more talented with language than I am. Lovers of geology found much to delight them in Reading the Rocks. She took the geological into the realm of the philosophical and political in Timefulness. This book (her third, a “pandemic project”) is a fun, trim little compendium of geological words. It relishes the exotic origins and fun flavors of geological jargon, and explores each word or phrase in a page or two, teasing out the big “take home” message in short order, and somehow managing to deliver cogent, coherent, condensed summaries of geological big ideas with a balance of economy and ebullience. Perhaps the best example of this is the short little “taglines” for each entry:
Examples:
Yardang Gone with the wind
Jökulhlaup Breaking the ice
Bioturbation The worm churns
I read the whole book (it’s only 168 pages) in two days, and I’m very keen on reading it again soon. I think I’ll quote passages from it when discussing komatiites and zircons, eclogite and pseudotachylyte. To me, one of the most striking passages was the entry on pedogenesis, the making of soil. You might expect an entry on dirt to be boring as hell, but she frames it in the context of how precious a set of circumstances are required to make soil – circumstances that cannot be expected on other planets, and only induced at great expense over vast spans of time. Those who would glibly “TERRAFORM MARS” would do well to spend ten minutes reading this trim little entry, which effortlessly guts their oversimplified vision. Earth makes earth very well, and we would do well to appreciate our home and conserve it rather than make a go for Plan(et) B. Marcia recently visited with my students via Zoom, and read us two passages from Geopedia: one on the Tully Monster, and another on a favorite topic: boudinage, which she illustrated using imagery from this blog! 🙂
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.