Quote du jour

“Strive to interpret what really exists.”
-Louis Agassiz

Triassic rifting in the Capitol

My girlfriend’s mom was in town in January, and we took her down to visit the Capitol Building. The tour had a good bit of history, but definitely missed the opportunity to talk geology. I was particularly struck by the columns in the Hall of Statuary:

Close up of one column, with my hand for scale:

That’s the Leesburg Conglomerate, a Triassic-aged deposit found in the western part of the Culpeper Basin of Virginia. (Technically, it’s “the Leesburg Member of the Balls Bluff Siltstone.”) The photos I showed readers in May 2008 were from the east side of Route 15, just north of Leesburg itself. The Culpeper Basin is a failed rift valley from the time of Pangea’s breakup. I say “failed” in the sense that it failed to become an ocean basin like the Red Sea or the Labrador Sea. While it may have failed to rend the metamorphic rocks underlying Reston, Annandale, and D.C. from the North American continent, it succeeded in accumulating continental sediments for two periods of geologic time, preserving a detailed record written in siltstones, conglomerates, basalt flows, diabase intrusions, dinosaur footprints and fish fossils.

Among the strata that the basin accumulated, the Leesburg Conglomerate stands out as the real rock star. It’s a gorgeous looking rock, a poorly-sorted and well-oxidized mishmash of (mainly) limestone chunks derived from the weathering of the young Appalachian Mountains. Visually striking as it is, it’s not surprising that someone tried to use it as a building stone. However, it’s not well-suited to being sculpted. Rumor has it that after countless episodes of pebbles popping out of otherwise pristine, finished columns, the column-carver swore he would never touch this particular stone again. To my knowledge, the Capitol’s Hall of Statuary is the only place in the world where the Leesburg Conglomerate has been used as a building stone.

Advice for giving a talk

What makes a good presentation?

I watch a lot of talks. Between monthly meeting of the Geological Society of Washington and professional meetings and student presentations and local departmental seminars, I see a lot of people present information aloud, with varying degrees of success.

I also give talks. While I don’t claim to be the best presenter in the world, I do know a good talk from a bad talk. I try to keep mine on the “good talk” side of the spectrum. Giving a talk, whether at a professional meeting, in a board room, or as just another day in class, is an act which is as much theater as it is information delivery. I’ve never taken a public speaking class, but I’ve got some real-world experience. Today, I’ve got some advice for anyone who’s going to be giving a talk. I’ll assume a traditional modern talk: a single expert speaker talking for half an hour or less, backed up by a PowerPoint slideshow. (“Expert” here means that you know something the audience doesn’t know. If that’s not the case, you might ask why the hell you’re bothering to give a talk in the first place.)

I hope the second-person style of this advice (“you, you you”) isn’t offensive to readers. Just imagine it’s an “open letter” to someone else, someone who you and I have just seen give a crummy talk.

Know what you’re talking about enough that you can speak extemporaneously. Reading from notes or an outline means that you (the speaker) are engaging with a piece of paper (or a laptop), and not with the audience. No notecards. You can use the images on your PowerPoint to guide your thoughts, but you should know the material, and the ‘trajectory’ of what you want to say, well enough that you don’t need some sophomoric crutch.

It should go without saying that one way to achieve enough confidence to speak extemporaneously is to practice: tell people at cocktail parties what you do, what topics you’re researching. Practice in front of the mirror. Practice in front of your spouse, your nephews, your pets. Practice with your peers, your professors, your students. Develop a full, robust taste for your presentation’s content that is independent of a particular string of words.

Look at people. Look your audience members in the eye, moving from person to person every few seconds. Do not talk to your PowerPoint up there on the screen. (Jess noted this in a similar talk advice post last September.)

Move around. The dynamics of a mobile speaker are much more engaging than a sessile speaker rooted behind some podium. I mean both waving your hands about, and physically walking around the room, forward and backward, left and right. Get close to people: like a magnetic field, human proximity is effective at making connections.

Use evocative language, including analogies, humor, precise vocabulary, pithy quotations, and the like. The spoken word is your medium, PowerPoint is your visual aide, and your expertise is your subject. Because you are delivering your explanations via the spoken word, you should use your words to sculpt a rich landscape for your listeners. Use active verbs like “wiggle,” “pierce,” “slam,” “jet,” “snap,” “rub,” and anything with a violent or sexual connotation. People pay attention to sex and violence; you can use these words as lures to draw them in to your subject matter. Also, vary the pitch of your voice. Anyone speaking in monotone clearly doesn’t care enough about their subject to get excited about it. The message to the audience is that they shouldn’t care either.

If you’re a ham like I am, then act it out. If you’re describing rocks getting squished, mime out being in a trash compactor. If you’re describing a cobble bounding downstream, jog a little slalom course across the room. If you’re talking about the position of dinosaur legs beneath their body (as opposed to say a crocodilian, where they stick out to the side), slump down on your belly and show what you’re talking about by contorting your own limbs in different positions relative to your body. Not everyone is comfortable with physical acting; some consider it demeaning to the dignity of the speaker, especially in staid, professional crowds. If so, that’s cool. But the audiences I have observed eat it up, professionals or not. It’s engaging and endearing.

It is okay to pause in silence while you gather your thoughts. Avoid nervously filling this pause with an “Umm” or an “Err.” Not only only are umms and errs 100% information-free, they ruin what could otherwise be interpreted as a dramatic pause, full of conscious intent. Good songs are not just a constant stream of words, they include slow bits and wordless bits and instrumental bits, all of which give the listener a chance to cogitate on their meaning. You’ll notice on “All Things Considered” or “Radio Lab” or “This American Life,” the producers insert little “buttons” of music, about 10 seconds long, in between information-rich pieces. Good presentations should be like that too, but unlike radio, you don’t have to worry about “dead time.” Your audience can see you, see your PowerPoint. They know you haven’t gone “off the air.” Better still, your pause gives people a chance to swallow your thoughts. Ramming information down their throats without a chance to chew it will not nourish them with your ideas.

Now for some specific advice about putting together a decent PowerPoint (or Keynote, or whatever) slideshow:

Use as few slides as possible to get your point across. Everyone is busy, and we don’t want our time wasted. Get to the point, and make it worth our time to be sitting there in your audience.

“Outline slides” are those that present your talk as an outline. (“First I’m going to give you some background on the problem, then I’m going to tell you about our research approach, then I’m going to interpret our results in terms of the dominant paradigm.”) In my opinion, outline slides are a waste of time. Clearly, any effective presentation is going to supply necessary background, describe what is unique about the presenter’s approach, and conclude by tying it back into the big picture. You don’t need to waste our time by outlining it for us. No decent movie or television show (including those about science), starts off with an outline! A shared outline is redundant to a well-constructed talk. If you’re a unsophisticated enough presenter that the only hope of communicating your intent is to repeat it via outline, then you shouldn’t be talking. Shut up and go back to your office; write it all down as a paper instead.

Use as few written words as possible. PowerPoint should be used as a slide projector: It is not an outline (or worse, a transcript) of what you intend to say. The worst presenters type out what they want to say, then read it aloud off the screen. This is an abomination of presentation. It is the antithesis of engaging your audience with your expertise. Ideally, all your slides should be imagery. There should be no slides of just text.

Use pictures. Use photographs. Use cartoons. Use graphs. Use data tables. Show movies. Show animations. Use visualizations. PowerPoint is a visual medium: use it for what it’s good for. Use it as a slide projector.

No sound effects, no fancy slide transitions, none of that stuff (“phluff,” as Edward Tufte called it). …Good lord, do I really even have to say that? Unfortunately, I think I do. I have observed people (students and bureaucrats, mainly) sometimes use these “bells and whistles” with what I suspect is an intent to distract the audience from a lack of content. Use of these features is an insult to your audience. No “clip art” either.

Use images at sizes at or below their inherent resolution. (i.e., not at sizes above their resolution.) In other words, if you find an image online that is good for your talk that measures 200 x 300 pixels, do not blow it up to 800 x 1200 pixels. It’s going to look horrible if you do that: pixelated and grainy and incredibly bad. I have seen some of the scientists I respect most give talks with these sorts of graphics — it looks like something a sixth grader might have thrown together. I find it shocking that someone so skilled in one aspect of their professional life could be so completely clueless in another. Even if you’re not capable of generating your own graphics, have a little bit of aesthetic sophistication.

Number your slides. If your presentation has 20 slides, your first one should have “1/20” tucked down in a lower corner, somewhere unobtrusive but obvious to anyone who’s wondering how much longer you’re going to go on. The second slide should say “2/20,” and so on. This gives your audience an orientation to your intended talk length, and they can then decide whether they want to keep sitting there, or whether their time would be better spent off getting a cup of coffee. One of the first things that I always do when I am watching someone set up for a talk is to steal a quick glance at their total number of slides. If they’re going to attempt to get through 55 slides in 20 minutes, then I know that either (a) they’re going to be going too fast for me to absorb the slides, or (b) they’re not going to be finished on time. A general rule of thumb is one slide per minute, though that’s flexible depending on your content and speaking style. Notice that numbering your slides does not do any good if you don’t say out of how many total that number is. In other words, seeing a “6” at the bottom of your sixth slide doesn’t help me estimate when you’re going to be done with your talk. (“Is that 6 out of 7? Or 6 out of ∞?”) Not that I’m not interested in what you have to say — but it’s unlikely I’m going to be rapt by your talk, smart as you are. My brain is going to be thinking about other stuff at the same time. Work with me here! Give me a sense of your plan for the next 20 minutes of my life.

End it cleanly, decisively, and preferably a little bit on the early side. Let us know that you’re done without saying, “Umm, …and that’s the end.” Think about the end to the most satisfying entertainment you’ve absorbed lately: a film, a song, the latest episode of LOST. You know it’s over without them having to spell it out by saying “…and that’s the end of this movie.” Asking what questions your audience has is a good fall-back ending statement, if you can’t think of anything more clever. Notice I don’t say “Are there any questions?” I say “What questions do you have?” Your expectation should be that your opus generates insightful, chewy interrogatives from those privileged enough to hear it. Clearly, any talk worth spending the time listening to should generate some thinking, some feedback. If it doesn’t, that’s a major red flag that you haven’t engaged your audience with your material.

OK: I’ve given all my advice to our nameless third-person lousy speaker. What else would you tell them? Chime in via the comments section below.

Crucifix site 3: a WTFite

So, I’ve introduced you to the sediments at the Crucifix Site, and the faults which cut across those sediments.

Today, I would like to show you something else that I found there, and ask you to tell me just what the hell it is.

Here we go: an outcrop of the volcaniclastic sediments in this area (stratigraphically beneath the Bishop Tuff), where you can find orb-like hollow structures in the weakly lithified rock. Here’s a couple:

Zoomed-in a bit on the biggest one:

I excavated it from the surrounding volcaniclastic sediments, and popped it out:

Rotated slightly:

I have a guess what’s going on here, but I’m by no means certain. Any ideas from the peanut gallery about what this strange thing is?

Crucifix site 2: Horsts & grabens

So, those sediments we saw yesterday? They’re faulted in the area around the Crucifix Site.

As this image shows, the style of faulting is normal faulting:

Annotated with some color to jazz things up a bit:

In normal faults, the upper block moves downward with respect to the lower block. They are typical of extensional tectonic settings.

Numerous small faults here — a little bit of displacement on each:

Ditto for this exposure (same place, just zoomed out a bit):

Nice! Two horsts and a central graben:

The normal faults exposed at the Crucifix Site are a lot like those we observe a kilometer to the north, up on the Volcanic Tableland. The difference is that the Volcanic Tableland faults disrupt the stiff upper layer of the Bishop Tuff (“Ig2”), while these Crucifix faults are smaller and more subtle — cutting through weaker stuff.

Crucifix Site 1: Sediments

On the September 2009 GSA field forum in the Owens Valley, the final stop of our first day was to check out the so-called “Crucifix Site,” along Chalk Bluff Road (north of Bishop, California, at the southern margin of the Volcanic Tableland). It’s called the “Crucifix Site” because there is a metal cross erected there:

This is the site of some pre-Bishop-Tuff volcaniclastic sediments. The place is interesting on several levels, including the sediments themselves, and the subsequent deformation they have experienced. Here’s a look at the outcrop:

Some annotations help to call one’s attention to primary sedimentary structures and interpretations:

Lots of the sediment itself was made of little beads of obsidian, usually surrounded with a “chalky” weathering rind:

A cool little channel cross-section was visible, too:

For some reason, this is what pops into my mind when I run into a well-exposed Cheshire channel cross-section:

Birds and wasps had tunneled into the softer layers, resulting in horizontal rows of holes. I tried to ignore these modern bioturbations so I could focus on the ancient tale in the rocks themselves. Some cool soft sediment deformation was visible, like these flame structures (upper part of the central gray layer):

Zoomed in on a pair of flame structures, and the down-sagged material between them:

…And another set:

This was odd: The lowermost layer (upon which my field notebook rests) is unperturbed, but the layers above it are all churned up in one small area (center), flanked by a couple of bird holes:

Zoomed-in on the area in question:

Annotated, for your viewing pleasure; green is top of undisturbed layer; red shows boundaries of zone of disrupted sediment:

I would be pleased to hear from anyone who knows more about sedimentology than me about the wavy bedding in the second (& third) photo, and this weird sediment disturbance in the lowermost photo. Also: with the flame structures, it looks like coarser material in the lower layer (gray) is the less viscous participant, while finer-grained (white) material is sinking downwards. Isn’t this the opposite of the way it usually works?

Virginia water well shows seismic waves

This site, from the USGS, shows depth to the water table for a well in Virginia:

You’ll notice the tidal influence on the water table (broad sine-curve-like up and down crests and troughs at ~12 hour intervals), and then a sudden perturbation which caused some wiggles almost two and a half feet of magnitude! This, presumably, is the seismic waves from the Chilean earthquake arriving — surface waves, I would guess, but I’ll happily be corrected if that’s not the case.

Major hat tip to Cian Dawson, who tweeted a link to the site around 6am D.C. time (which would be, what, 3am in California, Cian? Sheesh!). In the same tweet, a link to this hydrograph in Christiansburg, Virginia, showing its response to various historical earthquakes.

Frozen soil lifts off

When I was out poking around in the woods, confirming for local geophile Barbara that indeed her local geologic map wasn’t 100% accurate, I noticed this on the frozen ground:

We have seen this before, in a post back on NOVA Geoblog, almost exactly a year before I took this photo. Here’s another shot from the more recent excursion, taken a foot or so over from the first one:

What’s happening here is not that I am showing you particularly high-contrast photos of pebbles and cobbles in the mud. Instead, the reason for the dark line around the sedimentary clasts is that the mud is frozen. When water freezes into ice, it expands in volume by about 9%. This extra volume means that the ice can’t occupy the same space that the liquid water did. So it pooches upwards, as “up” is the direction in which it is least “hemmed in.” Down? No — the expanding ice is not capable of pushing the entire Earth out of its way. North/south? or East/west? Well, there’s already soil there, and it’s pushing back, so there’s no expanding out in those (horizontal) directions. So, “up” it is. That’s all we’re left with: “up” is σ₃.

If I were to draw this as a cartoon, here’s the “before” picture:

As the sheet of frozen mud expands upwards, it detaches from the non-expanding (in fact, shrinking, but not by anywhere near 9%) cobbles and pebbles. As the mud ice lifts up higher and higher, the gap between it and the clasts gets more and more pronounced.

Shadows in those gaps make them appear dark to the camera lens.

Ice pulls all kinds of neat tricks like this in the winter. What’s a cool ice phenomenon you’ve observed lately?

Piedmont rocks exposed in a creek

One of the cool things about being the local geoblogger is that people get in touch with you about local geology. Sometimes this even leads to meeting up for field trips. Here’s two quick photos from a recent (January 2010) field trip to a creek near Springfield, Virginia.

My host was Barbara X, a local aficionada of Piedmont geology. She has lived in this particular neighborhood for many years, and is very familiar with the local woods and drainages through decades of dog-walking there.

Her main question for me was “Could the geologic map of this area be wrong?” She showed me the map, and then took me out to an outcrop which clearly was of a different rock type than the map indicated it “should” be.

The offending intruder, a meta-basalt with two prominent joint-sets:

A short distance downstream, a cut bank revealed some saprolitic rock that is more typical of the Piedmont province:

I think we’re seeing bodies of schist/ gneiss (highly foliated in cross-section), as well as coarse-grained, lighter-colored bodies of granite. All of them have been weathered to hell: you can scoop handfuls of this “rock” out of the outcrop if you want. If you’re a plant, you can plunge your apical meristem right into it, and let the roots follow.

This is typical “outcrop” around here: though the mid-Atlantic region has a fascinating story (including the Appalachian mountain belt, like these rocks), the wet climate has rotted most rock away. The only other thing that’s worth mentioning about this particular outcrop are the upper-left-to-lower-right brown lines: those are fracture traces decorated with rust. The fractures serve as plumbing to move fluids around in the subsurface, and their dissolved cargo of elements can then react with the rock on either side of the fracture.

Rockies course applications open

For those of you who are potential NOVA students (really, that’s pretty much anyone on the planet), I wanted to let you know that applications are now open for the July 2010 Regional Field Geology of the Northern Rockies course that I co-teach with Pete Berquist of Thomas Nelson Community College. A more detailed description is available on my website.

Contact me via e-mail if you want more information or download an application here.

To whet your appetite, here’s Rockies 2009 student Jason Von-Kundra mapping Mississippian-aged carbonates in the Bridger Range of Montana: