Australian Christmas 2

This must have been written thirty years ago, maybe more. We're a tad more weary and wary now.

"Angels on the steps, shepherds on the grass," announces the liturgical lady.  "Joseph and Mary, are you ready?"  She scans the supply of angels and shepherds.  "Are there any more angels?"  She pauses, and calls again, trying to keep the traces of desperation hidden.

A few more small boys with tea-towels head-banded to their heads give off wrestling each other, a scattering of girls in party frocks with tinsel wreaths trickle away from their families, some of them a little doubtfully.  One or two are led forward by parents to take the hand of the Boss Angel and Boss Shepherd, both adults who look like seasoned campaigners at this lark.

It is 7.30 on Christmas Eve, the cicadas are shrilling in the trees, birds swoop in and out of the last of the sunlight, and overhead, flocculent clouds catch the first colours of sunset, and offer us a threat of storm that once again does not come.  Most years we get this threat, and most years it holds off.  About 700 people are gathered in the garden of a local church for an outdoor mass.

The Jesuit father told me when I phoned last night that this is the children's mass, but that is fine by us, even though it is obvious that he is working his way into a case of laryngitis.  Better that than a whisky priest, straight out of the pages of Graham Greene, working his way into a case of Scotch, I want to tell him, but I am uncertain how well his sense of humour will be holding.

The service is a simple telling of the story of Christmas, a few simple carols, and back into the streets just as the street lights are coming on.  We sit on the grass for the service: most people know to bring a rug, Chris and I are canny enough to bring low folding seats that give back support.

First, a messenger arrives to announce that Caesar Augustus has called a census, then Joseph and Mary, a young couple of the parish, walk along the path to several young inn-keepers, find their stable, and quietly produce "baby Jesus" (actually their daughter Anna, but that's OK, Jesuits are more relaxed about such things).  The three wise men pop in for a chat, and one of them is a girl, but that's cool as well.

Then the shepherds are called.  They arise, one scratching his rear in relief at losing contact with the grass.  The smallest shepherd panics, and runs for his family, and someone mutters something about the need for a sheepdog, but the lost shepherd is returned to the flock of shepherds, and they withstand the confronting angels.

The priest explains that with his laryngitis, he will need to be brief, and tells a short story about a boy who wanted to play Joseph, but was ordered to play the Third Inn-keeper.  On the night, he plays along, right up to the point where Joseph asks for a place to stay.  He pauses, then announces "She can stay, but you can get lost," he tells the rival who succeeded over him.  What is the meaning of Christmas, he asks.  Picking up Anna, he introduces her to us.  This is the meaning of Christmas, he answers.

By now the colours are mounting in the sky, the white cockatoos have fled, and a cricket has started chirping near one of the microphones, but it is all just part of a summer Christmas.  Then the mass is ended, and the priest announces that there will be small presents to those under 10.  There is a stirring of joy among the shepherds and the angels, but they are instructed to lead Joseph and Mary and baby Jesus out.  To the strains of "Joy to the World", they walk reluctantly away from where the three wise men are preparing to dish out small parcels of sweets.

There are trembling lips as they pass us by, for all the little heathens, the non-shepherds and non-angels are already lining up, and the shepherds and angels know well what the meaning of Christmas is to them.  Just as we finish singing, a small tidal wave of mixed angels and shepherds pours back up the path, where the three wise men demonstrate just how wise they are, by pulling up a reserve supply, especially set aside for the angels and shepherds who had all, it appears, been counted.  We adults leave, happy that children have not been disappointed.  To us, perhaps, that is the real meaning of Christmas.

School geology notes part 2

There appears to be a limit to the number of pics, so I had to split the entry in two.

  Once seen, never forgotten. Two examples of joints near Fairlight.

Geologists don’t really know how joints are formed, but they think it has to do with stresses being released as rocks above weather and erode away. And THAT brings us to weathering.

Weathering

All rocks break down in what geologists call “weathering”. This involves the decay of the rocks, combined with all the ways the planet has found for moving rock debris, erosion in other words, are both necessary for the rock cycle to operate. A lot of the most spectacular scenery emerges because some parts of the rock resist weathering, like Drawing Room Rocks near Berry, down the coast.

Here, the sandstone has accumulated an iron-rich layer near the top, but at a guess, water was able to get in through the joints, rock chipped away, and we ended up with this sort of pattern, with ‘occasional tables’.

In geology, nothing is completely permanent. For starters, there is no such thing as insoluble. Many of the minerals in rocks resist being dissolved, but over time, given enough time, no mineral is ever totally insoluble. Some minerals are rather more soluble, and if one mineral in a rock breaks down and washes out, it will only be a matter of time before the hard rock begins to crumble.

Air, heat and cold also play a major part in this breakdown, which is referred to as weathering. Geologists recognise two types of weathering: physical weathering, though this is sometimes called mechanical weathering, and this name probably tells us more about how it works.

All of the sandstone around the school shows clear signs of weathering. The sandstone face below and east of the library is a good example of one form of physical weathering caused by feet.

In 1969, just after major fires in the Royal National Park, I was sent out, in full ranger uniform, partly to see if the old tracks were visible, but also to ‘show the flag’. Where a track passed over sandstone, the path to walk was much lighter than the other rock: human feet had weathered the rock.

Lightning

There used to be a poor example of a lightning strike in the old nature area, but I think we lost that. No matter, it was unimpressive unless you knew what to look for.

   

Around the world, there are about 100 lightning strikes, somewhere, each second. That adds up to a lot of energy hitting things.

When lighting fails to hit a building, a tree, a foolish kite flyer or an unwise golfer, it usually hits rock. Lightning often comes with rain, and when the water has already soaked into a rock, the instant heat of a lightning strike turns that water to steam, flaking off a surface layer. Once the rock is in small pieces, other weathering effects can take over.

Note that these blasts happen on high places in storms. The traces are best sought for in good weather. If you are on a high place in lightning, move away! The danger signal comes when long hair starts to float up into the air, but by then, it may be too late…

And now for my favourite rock forms, which appear in the school grounds only in minor and beginning forms, visible only to a prepared eye.

Honeycomb weathering

Geology shapes our scenery, sculpting the rocks around us, and one of the delights of my home area is honeycomb weathering, sometimes called alveolar weathering by people of French background, while others call it fretting, stone lattice, or most poetically, stone lace.

Honeycomb weathering in Hawkesbury sandstone, some of it cross-bedded, near Box Head, north of Sydney.

Much of the best-exposed sandstone near Sydney is close to the coast, and around the world, it is common to blame salt spray for honeycomb weathering. The idea is that salt spray lands on and soaks into the stone, but when the water evaporates, salt crystals are supposed to wedge sand grains off.

There is definitely more to the picture and that, and while salt spray probably plays a part, as a young man, I saw honeycomb weathering in the Budawang Ranges, 40 km from the nearest sea coast. I have no surviving photographs from that time, but I do have something rather similar from the flanks of Uluru, on the far side from where the climbers used to start.

A curious but entirely natural weathering effect on the side of Uluru.

   

Ant lions

Ant lions were the first insects I ever studied, and they make neat pits in sandy soil. There used to be lots of them under the old demountables, and there should be some under the trees. They are the larvae of lacewings, alias Myrmeleontidae (Neuroptera). The name ‘lacewings’ describes their pretty wings quite well, but ‘ant lion’ is a good name for the larval stage. Instead of hunting like lions though, they dig pits in the sand and sit at the bottom, waiting for an ant to fall in.

I once saw one of these animals capture a small weevil, but usually, they eat ants. Whatever the prey is, once the unlucky animal reaches the bottom, the ant lion seizes it in its pincers and sucks it dry. In the end, it flicks the empty husk of the prey out of the pit. Ant lions are neat!

To find these curious creatures, look for a small conical pit, 1–3 cm across in dry sandy soil. The soil may be close to one of those gum trees with sap that kills grass, or inside a hollow tree, along the edge of a building or under a rocky overhang. Sometimes, you can even see ant lion pits, right out in the open in the dry season on Cape York, in the summer around Myall Lakes in NSW and in dry areas. All they need is dry sandy soil.

A large ant lion can be 6 mm long, but 1.5 mm of that length may be the nippers that it uses to seize its prey. It digs a pit by backing into the sand and moving in a circle, flicking sand out with its head. Recent research on fossils in amber suggests they have made pits for 100 million years.

Dry sand only piles up to a certain slope, called the angle of rest, and this is the slope of the sides of every pit. At this angle, the sand is unstable and ready to tumble down if a small animal walks near the edge. As soon as sand grains hit the bottom, the ant lion starts flicking sand up from the bottom of the pit. Some sand falls down again, knocking its prey down the slope, but if the ant lion flicks enough sand out from below, the whole slope begins to slide down, carrying the food animal with it. Ant lions are easy to keep but they aren’t geological.

A moral tale for kids:

Whenever people in the outback dug a well in a sandy river bed or climbed a dune, they were in the same position as ants, except that there was no monster waiting to grab them and suck them dry. The real danger came as they dug down close to water, because damp sand will hold together, and they could dig a steep-sided hole. Then when the sand dried, it would collapse.

Each year in Australia, one or two children are killed when a sand cave collapses on them. No explorers were ever killed that way, but probably a few needed their companions to dig them out.

As you can see, in science, everything is connected. We teach them to read the rocks, and weave a web around them!

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A small advertisement: some of the illustrations appearing here will be in my upcoming Not Your Usual Rocks. This is now moving into final editing, and will either be the subject of a contract for a coffee table book by mid-June, or it will be issued as a delicious e-book by April 2020.

School geology notes part 1

I work as a volunteer 'visiting scientist' at a local K-6 school, and the last two years have been turmoil as it was rebuilt to meet climbing population figures. In the process, some beautiful nature was destroyed, but the place is bouncing back, and I saw that there was now some exciting sedimentary geology to play with.

Today was the last day of the year, and I was there to show the teachers what is available to use, and I wrote these notes before I went.

Stories

Rocks tell stories, and some of these stories are at a simple THE CAT SAT ON THE MAT level. Other stories that the rocks have to tell are more like Virginia Woolf on a bad day.

Getting kids started on reading is a bit like edging them onto a slippery slope on a bicycle and keeping them on an even keel as they get up to speed, carried along by natural forces. OK, that’s a stretched analogy, but slippery slopes are one of my long-term temporary obsessions. All you need, in order to play is a sand dune, but a Vegemite jar half full of sand will do as well.

Once seen, never forgotten: I had to learn this sort of stuff for myself, but each bit, once I acquired it, became part of my ongoing observations. The linking theme here is that sand that is piled up collapses to form a fixed angle (for that sort of sand), and that angle shows up in dunes, rocks, sandbanks, pits and holes in dry sand and more.

When we try to pick out anything by itself, we find it hitched to everything else in the universe.
—John Muir, My First Summer in the Sierra, Boston: Houghton Mifflin, 1911, chapter 6.

A slippery slope in a jar

The thinking for this began when I had an idea to try something. I was getting ready to work on the track with Stage 2, I think. Our topic was flowers and stuff, but I spotted the rock on the right, and saw one of my favourite simple stories: current bedding or cross bedding.

I will explain what that is shortly, but let’s walk before we gallop down the slope, OK? Just watch how all of the bits come together, in the end.

Advancing dune, Sahara

Ant lion pit, coin for scale

Current bedding, as I prefer to call it, tells us something odd about sand. If you tip dry sand out of a funnel in the sandpit, it will

form a conical pile, and I can predict to within a couple of degrees the angle that the sand will lie at. We call this angle the angle of rest, and that’s the last bit of jargon.

Angle of rest in a jar. Use a cylindrical
and clean, very dry sand.

Ant lions (I will talk about them later) make pits in dry sand, like the one on the left, and the sides also lie at the angle of rest, as does the front of an advancing dune in the Sahara.

So there I was, clutching a Vegemite jar, half full of dry sand. I always carry this in case somebody happened to need a jar of dry sand, and a full jar is too heavy… I bounded onto the rock, declared that I was sitting on a 205 million-year-old fossil, then moved among the kids and showed them the jar, rolling it.

I explained that when sand is pushed along by wind or water, it gets pushed over the front, and this creates (drum roll please!):

Current bedding

Once you know what you are looking for, it’s everywhere, and any kid who has been shown the secret will be able to share it with others. Any cutting, any cliff is likely to reveal beds of sandstone, laid down as sand banks: the picture geologists have of Sydney in the Triassic (~205 million years ago) is a giant sandy river delta, a bit like Bangladesh today.

Three examples of current bedding: (top) Old Man’s Hat, Inner North Head; (centre) Sydney Road Fairlight, Manly side of the shops; and Malabar.

The shots above are easy to spot: the ones around the school need a trained eye. Let the training begin!

(A note to my teachers, less relevant to others: In all of these shots, I have left background in place, so you can come back and look at them.)

 

 

 

 

 

As you can see, the layering is more subtle when it comes to bush rock. The right-hand shot éabove is on the cycle track, and every cyclist going along there is running over 205 million-year-old fossils.

But how do we know the age? We don’t, not really, but the rock is Triassic, making it between 180 million and 220 million, and the sandstone is early to middle Triassic, so 205 million years is near enough for government work. Talk to me if you want more, because explanations require lots of hand waving..

 

On the western side of the school, the sawn stone has nice banding, and this is a Virginia Woolf sort of story, so here’s the Classics Illustrated/Cliff Notes version/. Iron occurs in compounds in two forms that old chemists called ferrous, which is soluble and ferric which is insoluble.

Banded iron in sandstone.

The ferrous form is now called Fe²⁺, and the ferric form is Fe³⁺. The key thing is that one can change into the other, Fe²⁺ seeps away, but when it changes to Fe³⁺, it stops where it is. Chemists say that iron II is oxidised to iron III and iron III is reduced to iron II.

Iron banding and Liesegang patterns

I didn’t find any Liesegang patterning around the school, but this is the same iron II/iron III story.

     

The same explanation applies to the iron banding we can see, and some of that is spectacular:

 

Joints

I was tricked when I thought I had found a joint in the sandstone. Joints are planes of weakness that are seen in most rocks, but they are particular important in the shaping of Sydney, because when sea levels fell, streams and rivers were directed along the jointing patterns, which is why the city has so many east-west and north-south valleys.

When the sea rose at the end of the last Ice Age, it flowed into those valleys, and we say that the fern leaf pattern of the harbour is a drowned river valley. Anyhow, those ‘joints’ were cut with a saw, but they give you some fresh rock to look at. There are no joints that I can see in the school grounds now, but below are some local joints:

  

Above: three examples of joints: (top) Old Man’s Hat, Inner North Head; (centre) Sydney Road Fairlight, north side; and on the way to Fairy Bower.

There appears to be a limit to the number of images I can insert, so this is continued in part 2.

The naming of things

I will keep this brief, and trust that those who can tell a clade from a handsaw will treat any inelegance as a result of my seeking to be concise rather than precise.

Every scientific name has two parts, the genus and the species. Unrelated animals cannot share the same genus name, and the first-named takes priority: Platypus, the name given first to a beetle and later to an Australian mammal, now only means the beetle—in science. Scientists now call our “platypus” Ornithorhynchus, but Australians couldn’t be bothered.

Lesueur's image of platypodes (or platypuses):
I never would cry
"Two platypi!"
Respectable bodies
Say "Platypodes".

One of our friends from the North Head Sanctuary.

Australia’s other monotreme, which we call the echidna was named Myrmecophaga in 1792. Unfortunately, that was the name of a South American placental ant-eater, so the name would never do for the unrelated Australian monotreme.

The French scientist, Georges Cuvier suggested calling it Echidna, which was the name of a serpent in Greek mythology. Sadly, this name was later found to have been given twenty years earlier to a moray eel, and so the animal ended up being called Tachyglossus, except with Australians, who had already adopted ‘echidna’ as the common name, and stayed with it. (That is, the scholars called
them ‘echidna’: the common folk knew them as the spiny ant-eater and in the same way, the platypus was the water mole.)

According to legend, a cask reached Newcastle-upon-Tyne Literary and Philosophical Society in late 1799. It was sent to the society by a new corresponding member, John Hunter, at that time the governor of New South Wales. The cask was filled with spirits, a platypus (at that stage unnamed) and what Hunter said was called either a womback or a wombach.

A woman servant was carrying the cask on her head, when the bottom of the cask caved in, drenching her in smelly spirits, a chunky wombat and a platypus that, to an untrained eye, must have looked like a creation of the devil.

We know the name wombat must have become known only in 1798, because an expedition of convicts returned to Sydney in February of that year, and mentioned dining on ‘a kind of mole’: it was what we would call a wombat.

The leader of the expedition, a former convict named James Wilson, was also an initiated man of an unidentified Aboriginal tribe, near Sydney, and it was probably he who provided a local name wombach for the ‘mole’.

One of the earliest images of a wombat, prepared in London and quite wrong.

Even in the 1850s, people wrote about the “Phascolomys wombat of Péron et Lesueur”. In reality, that name was given by Lesueur & Petit in 1808. Joachim Johann Otto Voigt had already described it as Didelphis wombat, but the genus Didelphis includes the North American opossums which are marsupials, but not very wombat-like, so a new genus name would be needed, once people looked at actual specimens.

Even earlier, in 1800, probably working from the specimen that fell on the servant’s head, zoologist George Shaw had described it under the name Didelphis ursina (meaning ‘bearlike possum’). He called it the “largest of all the Opossums”. Note the species name, because that part survives to this day.

Now the tricky bit: another French scientist named Geoffroy managed to give the wombat two separate genus names in two years, 1802 – 3 and 1803 – 4. (He used the new revised Republican calendar, and these were years 11 and 12 on that scale.) Whichever way, he got in first, dubbing it Vombatus in year 11, and Phascolomis in year 12.

Geoffroy does not appear to have given a species name, but that matters little because Shaw had assigned a species name two years earlier, and that was still legitimate. So we use Geoffroy’s genus, but the common wombat is Vombatus ursinus today (the last tricky bit is that Latin names have a built-in gender at the end, and so ursina had to become ursinus to match the masculine Vombatus). It took some time for people to stop calling the wombat Phascolomis or Phascolomys, but it did happen, eventually.

Backobourkia sp.

One thing that taxonomists have learned is that you must look up your planned name to see if it is free—or choose a name so way out that nobody could possibly have used it, hence fossils called Montypythonoides and Thingodonta, and a spider called Backobourkia, from 'Back of Bourke', Australian vernacular for seriously way Outback. This engaging creature is found near my home in Sydney, far from the Outback.