Basin and RangePosted: April 30, 2012
Can you honestly say that you knew exactly what you wanted to be when you were a child? I can.
I guess I should have seen the signs ahead, my Mum and Dad giving me books on geology as a child, and fossil hunting in Northumberland. Some of my happiest memories involve clambering around, and falling off, rocks. The thing that really sealed my fate was one time when Dad came back from some engineering work in the Outer Hebrides. We were sat in the car, high up in the Campsie Hills, overlooking Glasgow, and he handed me a present. A lump of Lewisian gneiss. The rock showed its history in its density and appearance. You could tell instinctively that this rock had been mangled, buried and heated, deformed and reformed. I almost expected it to still be warm. That feeling has never left me, and from that moment on, I was a goner.
Photo of Lewisian Gneiss, from the Geowalks blog – read it here.
You’re probably wondering what this has to do with “Basin and Range”. Well, there are some books that written that distil the essence of a particular subject. This is one of them. If I ever tried to describe the wonder of geology, this would go a long way to explaining it. John McPhee gets it. I mean, really gets it. Better than that, he can put it into writing. No wonder the guy won a Pulitzer prize.
Basin and Range describes a series of trips McPhee made with a variety of geologists across America, from grad students to professors. He was interested in constructing a geological history of America, based upon roadcuts and other places where the inner workings of the earth could be seen.
The book starts at the western edge of the George Washington bridge in New York. He describes the formation of the Palisades Sill, and the geology out to the west. The geologist that he is with uses a phrase that strikes a chord with me:
“If I’m going to drive safely, I can’t do geology.”
Yes indeed. I find it difficult to drive through roadcuts and past interesting geological features without becoming quite distracted. I’ve learned that it’s far safer to stop and then gawp!
McPhee talks about looking at one particular Interstate that runs across the entire country, and what sorts of geological boundaries it would move through. Interestingly though, he overlays that with additional boundaries, those of creatures. One lovely expression he uses is describing the centre of the US as a drawer, much as you would find in a desk:
“…really a quartering of a continent, a drawer in North America. Pull it out and prairie dogs would spill off one side, alligators off the other – a terrain crisscrossed with geological boundaries, mammalian boundaries, amphibian boundaries: the limits of the world of the river frog, the extent of the Nugget Formation, the range of the mountain cougar.”
McPhee’s writing has a poetry to it. If he was writing about licking postage stamps, it would still be fascinating, and you would probably want to go off in search of some to lick yourself. Describing the language of geology, he uses some of my favourite words and phrases, including “radiolarian ooze” and “clinoptilolite”, and explains to the reader the subtelties of things they probably take for granted. All granite is just granite, right? Wrong. In an accessible way, he shows why geologists have so many different terms for particular rocks, and also the idea that samples of the same liquid rock will turn into different rocks if allowed to cool below or at the surface. They might chemically be the same, but they’re not the same rock any more. Lovely.
I also like his way of visualising what particular places might have looked like, hundreds of millions of years ago.
“You cross the Newark Basin. It is for the most part filled with red mud. In the mud are tracks that seem to have been made by a two-ton newt. You come to a long, low, north-south trending, black, steaming hill. It is a flow of lava that has come out over the mud and has cooled quickly in the air to form the dense smooth textures of basalt. Someday, towns and landmarks of this extruded hill will in one way or another take from it their names: Montclair, Mountainside, Great Notch, Glen Ridge. You top the rise, and now you can see across the top of the basin to the Border Fault, and where Whippany and Parsnippany will be, some thirty miles west of New York – there is a mountain front perhaps seven thousand feet high. You climb this range and see more and more mountains beyond., and they are the folded-and-faulted Appalachians, but middle-aged and a little rough still at the edges, not caterpillar furry and worn-down smooth. Numbers do not seem to work well with regard to deep time. Any number above a couple of thousand years – fifty thousand, fifty million – will with nearly equal effect awe the imagination to the point of paralysis.”
This kind of writing fired, still fires, my imagination. The world we know is a place of constant processes, as he describes. Mountains are being uplifted at the same time as they are being eroded. It’s not as if only one process can take place at a time. The names of places that they travel through and talk about are marvellously evocative, Wind River Canyon, Thermopolis, the Sonoma Range, Old Dad Range. When he describes long valleys running for a hundred miles north into the darkness, I want to jump into a pickup and drive through the mist rising from the streams, and follow the thin lines of telephone poles, not knowing what I’ll find next. The sheer scale is something that I love about the United States. It isn’t just big, but truly massive.
Part of my enjoyment isn’t just the subject matter. McPhee has a distinctive turn of phrase. For example, when he is in Nevada, he describes the silence of some remote place:
“Silence – a great spacial silence – is pure in the Basin and Range. It is a soundless immensity with mountains in it.”
When he talks about geological processes, he notes again and again that things don’t quite happen in the way that “Old Geology” teaching says. It isn’t a case of mountains being formed, and then eroded. Where the Pleasant Valley abuts the Tobin Range, he describes where a fault of 16 feet width appeared, separating trees that used to stand together. Given that the mountains were being eroded at about an inch per century, this represented a “leap” of about twenty thousand years, in an instant. He also points out that what you can see in Nevada, in the Basin and Range province, is what is visible during mountain-building.
Most of the rest of the book gives a good recounting of geological theory and practice over the last two hundred years or so, but his description of the welded tuffs of the Basin and Range deserve mentioning. This rock type was what was on the ground when the faulting that created the Basin and Range began. When most non-geologists think about mountains being formed, they think about collisions betwen plates, like a rucked-up carpet. This works for ranges like the Himalayas or Appalachians. The Basin and Range is a bit different, in that the land is being stretched, or drawn apart. Before all of that happened though, the welded tuffs were formed. Blinding hot ash erupted from vents in the land surface, blanketing everything for miles around with material hot enough to weld. McPhee describes this as being far thicker and denser than the ash that consumed Pompeii. The great heat caused the material to weld itself into a solid glassy material. Naturally, every living thing in the region died. Things stayed this way for about twenty million years. Twenty million. Humanity has been around for about two million, for comparison. For ten times that length of time, the welded tuff basically sat around and was eroded by the weather. When the tuff is drawn apart, the fault blocks tip, and are eroded, forming mountains on one side, and lakes / depressions on the other. Thus, the Basin and Range province of the title is formed.
One of the most significant events in the history of geological thought came when James Hutton observed an angular unconformity near Jedburgh, in the Scottish Borders. At that point, nobody really had a clear idea of how old the Earth actually was. The Church had put forward an estimate, in the shape of James Ussher, the Archbishop of Armagh. He had totalled up the ages of various people in the Bible, and stated that the Earth was created in 4004 BCE. OK, on one side, we have the age of the Earth as about six thousand years, and nothing from the geologists. When Hutton was looking at his unconformity in the Borders, he was looking at sandstone sitting roughly horizontally on top of another kind of rock called schist, which had been tilted until it was sitting almost upright. Being of a scientific mind, Hutton had been wondering about the speed of geological processes like erosion as he looked at his fields. He worked out that slow processes, repeated over very long times, could give really big effects. Mountains can be eroded, one sand grain at a time. It just takes (forgive me) a geological time scale. The unconformity was where two very different kinds of rock were sitting next to each other. He reasoned that the first (schist) rocks would have to have been formed, and then eventually tipped up until they were almost sitting on their end. Erosion would have to take place, giving a more or less flat surface, and then the sandstone would be formed, ever-so-slowly. It became clear to him that the Earth could not be only six thousand years. Geological processes could explain how different kinds of rocks formed, without having to invoke strange theories like granite precipitating out from water, or Divine intervention. Some people ridicule Archbishop Ussher’s effort to calculate the age of the Earth, but to be fair, he was following a fairly logical process, given the data that he had available in the Bible. Getting back to Hutton and his “eureka!” moment in the Borders, there is a similar place described in the book, in Carlin Canyon, Nevada.
Naturally, this caused something of a stir in the scientific and religious spheres. Hutton was not helped by the fact that his writing was difficult to follow, even for geologists. McPhee gives a page of so as an example, and if you can remember what he was talking about by the time you reach the end of the (massive) sentence, you’ve a better memory than me! Luckily for him, he had friends who could write in a much more accessible style, allowing people to understand what he was actually getting excited about.
An alternative school of thought proposed that rocks were precipitated from water, and divided up into Primary, Secondary and Tertiary rocks. While this approach has now been dropped, it is curious to note that we still refer to rocks of a particular event as “Tertiary volcanics”. This is a throwback to an earlier time and way of thinking.
McPhee’s book moves onto more recent geological theories, including plate tectonic theory. Until the twentieth century, we didn’t have a really clear idea of how bit of the planet could move around. he crustal blocks are now referred to as “plates”, such as the Atlantic Plate, the Nazca Plate, or as sublime proof that geologists do have a sense of humour, the China Plate. A number of innovative scientists, including Rear-Admiral Hess, Heezen and Tharp, and Vine and Matthews came up with pieces of the jigsaw, namely that the Earth’s magnetic poles switch over regularly and the oceans act as recycling centres for the crust, being created in one area, and destroyed, or subducted, in others. While the oldest rocks on the surface of our planet have been dated to almost four billion years of age, the oldest seafloor sediments are Jurassic in age, about 140-195 million years old.
For an excellent look at plate tectonics with the US Geological Survey, click here. Non-geologists, don’t be alarmed. It’s really well written for normal people, and worth a good look, as I’m painting with quite broad brush strokes!
The end of the road trip comes in Lovelock, Nevada, with the thought that if the geological activity in the Basin and Range continues for a while (geologically speaking), the ocean will pour into this region, forming a new sea. The then mayor of the town said that it would make a change, having water after so long without. Sitting in a small western town as a train rumbles past carrying aircraft engines, they sketch out the presumed extent of the sea that might be a long time coming.
Journey’s end – Lovelock, Nevada
I would rate this as one of the best books I’ve ever read. It certainly inspired me to become a geologist, but even if I hadn’t, it did open my eyes to what McPhee and other Earth-scientists refer to as the Big Picture. Reading it again, more than twenty years after I sat with it as an undergraduate student in St-Andrews, Scotland, I felt the wonder anew of the world that we all inhabit, and the sheer scale of it all. Humans are like insects. We could wipe ourselves out, and ten million years later, everything else would be like new. As another author once said, Earth abides.