Search This Blog

Tuesday, 10 September 2019

What geologists think, part 3

8. The standard principles of science

These are ideas that all scientists just assume, but they are rarely stated explicitly for students or the public. There is enough information here to tell you what each idea is about, and you will find enough terms to let you look the idea up, if you need to. There are lots of ins and outs, and working scientists spend their lives mastering them. They will, I hope, recognise that this is Science Lite.

Atoms and molecules

All matter is made up of atoms, and the properties of any piece of matter will depend on what atoms are present, and how they are arranged and connected. Many atoms join up to form regular frameworks that we call crystals. Sometimes, atoms join into tight standard groups, like water, quartz, salt and sugar. We csll these groups molecules.

The laws of thermodynamics

For general purposes, heat flows from hot to cold, perpetual motion is impossible, and there is no such thing as a free lunch. By the way, if you want to drive a politician or an arts administrator to distraction, ask him or her to explain (or even just to state) the second law of thermodynamics. Trust me: it matters!
A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare’s?
—C. P. Snow, Rede Lecture The Two Cultures and the Scientific Revolution (1959).
 If you want a simple version, it says that differences in temperature, pressure, and density tend to even out, after a while. More detailed discussion involves entropy The simplest available version of that: entropy is a thermodynamic function that measures randomness or disorder. If you like, entropy is a measure of untidiness.
Most of the principles of science are what scientists call counter-intuitive. In lay terms, they seem to go against our gut reaction; the earth as we experience it looks flat, and our intuition tells us the sun and moon circle around us once a day, but ignoring intuition, all scientists agree that the world is a globe, we orbit around the sun, and the moon orbits around us once a month.

Entropy is slippery, rather than counter-intuitive, and you have to note the qualifications which limit entropy to inside a closed system. Under those conditions, entropy, or disorder, increases, which is how scientists say that over time, everything gets more random, more dispersed.

There can be no exceptions to the rule that entropy, the disorder of things, always increases, but life, at a local level, can be an anti-entropy agent, making some things more ordered at a local level, even as entropy is increasing on a larger scale. In simple terms, animals and plants gather up and concentrate certain elements in our bodies.

Across the universe, every change leads to an increase in the total entropy, but the delight lies in the details, and a lot of geological science comes down to explaining how, on a local level, the process of concentration in elements or minerals is driven.
If [your pet theory of the universe] is found to be contradicted by observation—well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.
—Sir Arthur Stanley Eddington, The Nature of the Physical World (1928), chapter 4.

Conservation of mass and energy

In simple terms, matter and energy can neither be created nor destroyed. There is No Such Thing As A Free Lunch.


As a rule, things are in balance, but that is not the same as saying they are unchanging. The number of oxygen molecules in an open jar may vary slightly over time, as molecules whizz in and out, but at any practical level, the entries and exits cancel each other out. If I have crystals of salt sitting in a saturated brine solution, some of the chloride and sodium ions in solution may attach to the crystals, but on average, just as many ions will leave the crystals. We say the solid and the solution are in dynamic equilibrium.

The law of large numbers

There is no such law, but it is convenient to pretend that it exists. Given time, every atom of a sample of radioactive carbon-14 will break down. We cannot say when a given atom will decay, but with large numbers of atoms, we can say that half of all of the atoms that we start with now will have decayed if we come back in 5730 years from now. We say that carbon-14 has a half-life of 5730 years.


Evolution also hangs on large numbers. You won’t evolve, I won’t evolve, but our species, like every other species, does evolve. Don’t worry: some of your genes will carry forward, and some of them may be more common in a future population.

(I anticipate, for example, that in a thousand years, the descendants of today’s Australians will have a skin color darker than mine, due to the selective effects of melanoma.)

(Note that this can  be negated because humans, uniquely in an evolving world, can apply social changes to limit selection effects.)


Every part of science is able to be falsified by evidence, and if some idea can’t be tested and potentially falsified, it just isn’t science. That doesn’t mean science is all false, it just means every assumption is always considered open to testing and being found wrong.

If we found dinosaur fossil bones and human fossil bones in the same rock, this would mean we probably had to revise large parts of what we think we know about geology and biology, though the first step would be to check carefully that somebody hadn’t just pulled off a hoax.

Scientists are always on the alert for contradictions like that, even though they don’t really expect to find any. One way to become a famous scientist is by finding a red-hot contradiction to what everybody believes.

Ockham’s Razor

Then again, maybe we wouldn’t need to revise anything. William of Ockham made it a lot more complicated, but his basic notion was that if there are two possibilities, you should take the simpler one. If we found human and dinosaur fossils in a single rock, a simpler explanation would be fraud. We would at least look for evidence of fraud first, but if there was truly no evidence of fraud, it might be time to start a rethink.

9. Caveats

I am not a geologist, but I know how to think, where to look, and what questions to ask. My undergraduate studies were mainly in the areas of botany and zoology, so I may, from time to time, be in error. As a professional science writer, I am used to checking my facts, but even when I get the latest opinions there is still one gotcha remaining.

Science changes, and geological science does change—and I saw it happen. When I was an undergraduate, I picked up one year of formal geology training, enough to appreciate that the rocks yield the soil that my precious plants flourish in, plants that feed my equally precious animals.

One day, one of our geology lecturers urged us to attend certain sessions of ANZAAS, the Australian and New Zealand Association for the Advancement of Science. “Listen to Sam Carey,” he told us. “He’s quite mad: he thinks the continents are moving.”

That was in 1962, and I did indeed hear Sam Carey talking about such wild ideas. He seemed to make a reasonable case, except that we all knew the idea was crazy. Just three years later, plate tectonics was all the go.

In fairness, Sam Carey was only partly right, because his notion was based on some false assumptions, but the key thing to note is this: in 1962, moving continents was madness, by 1965, it was pretty much the orthodox model.

I have tried in this book to stay with the best and safest bits of orthodoxy, but at any time, that which was orthodox can be defeated of overturned by a simple paradox. One new discovery is all it takes, as T. H. Huxley said while discussing historical work on the spontaneous generation of life:
But the great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact—which is so constantly being enacted under the eyes of philosophers, was played almost immediately, for the benefit of Buffon and Needham.
—T. H. Huxley, Presidential address to the British Association in September, 1870.
My book (meaning Not Your Usual Rocks, still to be published) is about the facts—though I will later discuss a maverick theory about the origins of oil. I don’t believe it, but it is both entertaining, and instructive to consider as a way of seeing how science works.

By the time you are done, all of these will make perfect sense.

My book wins a prize.

Note: the book won the prize, not me, though I was part of the team at the National Library of Australia.

The guilty parties include:

  • Author: me;
  • Commissioning Publisher: Susan Hall;
  • Editor: Joanna Karmel;
  • Designer: Stan Lamond;
  • Illustrator (cartoons): Tony Flower;
  • Image coordinator: Emma Posch;
  • Production coordinator: Melissa Bush;
  • Indexer: Joanna McLachlan.

The award was part of the Educational Publishing Awards 2019, and it came under this long-winded category:

Student resource: Arts/Science/Humanities/Social Sciences/Technologies/Health and Physical Education/Languages

Anyhow, here's what it looks like, front and back:

Tuesday, 3 September 2019

What geologists think, part 2.

As I said before, I'm cleaning up all the unfinished projects, and Not Your Usual Rocks is at the top of the pile.

You'd probably be better off starting with Part 1, but there are two by-the-ways

1. The photos that aren't credited are mine, and they are all
© Peter Macinnis, Creative Commons Attribution 4.0 International.
That means you can use them for non-commercial purposes with attribution, but while I squash thieves like the people at the Charles Sturt Memorial Museum, I will happily provide high-res copies to people who ask.

2. The locations reflect a lot of travel, but you can probably work out roughly where I live, if you live near me. If you do, say g'day!

6. All of the effects we see in the geology can be explained

Basically, all the things that we see in the world can be explained by the forces we see operating today. Geologists call this principle uniformitarianism, and it just means the natural laws and processes that we see shaping the earth today are the same ones that shaped the past.

In other words, we don’t work on the principle that there used to be wizards and witches who moved the rocks around; there were no fire-breathing dragons that made the lava melt. We do not need to assume the existence of pixies driving Stealth Bulldozers, poltergeists with geological interests, malignant mammoths, whimsical aliens or lost civilisations.

Continents move, floating on the surface of the planet; earthquakes happen; rocks form, weather and erode; rocks get pushed up; others get pushed down and buried, and so on. On a smaller scale, sediments get washed by water, blown by winds, and sometimes, pushed by glaciers.

When weight is applied to the existing surface, in the form of glaciers or any other way, the earth’s crust behaves like a small raft that an elephant has boarded: the rocks sink. On the other hand, when glaciers melt, the earth springs back up again, and this is currently happening in Scandinavia which was relieved of a lot of weight, about 10,000 years ago.

The rocks, even the not-your-usual rocks, keep to the following principles.

7. There are standard rules of geology

Sometimes, what you see may appear to be contrary to these rules, but if you think that, it usually means you haven’t thought hard enough. The apparent contradictions emerge only because you are unaware of the other rules that applied in a particular place. With enough thinking, you can generally explain what you see.

Rocks are usually laid down in flat layers.

It is a fairly safe rule that sedimentary rocks form flat, parallel beds, because the sediments are washed or blown into some sort of basin, and the first material fills in the gaps and crevices, leaving a flat surface. The effects of currents (or winds) and gravity keep the top fairly flat.

Horizontal strata, Bungle Bungles, Western Australia

An illustration from Charles Lyell’s The Student’s Elements of Geology (1871), page 17, showing how irregularities in an underlying surface are filled in, slightly contradicting Steno. [Public domain]
Then again, some beds can be laid down on a slope. This is called cross bedding or current bedding, and we will look at it in more detail later. Cross bedding can be distinguished from beds that have been tilted later by looking at the horizontal beds above and below.

Cross bedding in Hawkesbury sandstone, Old Man’s Hat, North Head, Sydney, Australia
There can be traps for the unwary when it comes to igneous rocks. If the rock arrives as lava, streaming down the flank of a volcano, some of the lava cools and becomes solid, leaving a sloping skin of rock. Nothing is inexplicable.

Eroded remnants of an old volcano near Cape Palliser, North Island, New Zealand.

Younger rocks usually lie on top of older ones

They are always laid down that way, but there are a couple of notable exceptions. Basalt sometimes pushes up through sedimentary (or other) rocks to form a dyke. If the dyke reaches the surface, it flows out over the landscape (which is why it is called a flow. A flow is always younger than the rocks it lies on top of, and older than any rocks which are found above it.

Sometimes, the basalt pushes in between two layer of rock, forming what is called a sill, but the basalt remains younger than the rocks that lie on top of it. How do we know? We look for contact metamorphism, above and below.

The other exception to youngest-on-top comes when rocks bend, and fold, and sometimes (rarely), overfold, so that the usual age order is reversed in a limited area.

In less extreme cases, horizontal beds may just be tilted up and eroded away, leaving tilted rocks behind. If the land sinks at this point, new sediments wash in to start a new age of rock building.
In an area where there are active volcanoes, lava may pour out and flow across the countryside, laying fairly flat layers—except, as mentioned above, on the flanks of the volcanoes, where sloping beds will form.

The Columbia River forms the border between Washington and Oregon in the USA, flowing through a valley carved through a massive series of basalt flows.
There can be gaps in the geological record in any place

On my home territory, near Sydney on Australia’s east coast, the rocks are Triassic in age. If you drill straight down you will come eventually to Permian rocks, the coal measures that are exposed around the margins of what we call the Sydney Basin. You find coal at Newcastle, Wollongong, Lithgow and other places. Coal also used to be mined on the very shores of Sydney harbour, but they had to sink a shaft quite a long way down, all the way to the Permian rocks.

In theory, if we keep going down, we should next move into rocks from the Carboniferous, but these layers are missing in my favourite walking area, in the Budawang Ranges, west of Nowra, south of Sydney. We meet up with tilted Devonian metamorphic rocks instead. It looks as though we are missing 100 million years (or more) of geological history.

Any rock-hound will tell you this is an unconformity, and hazard a guess that the Devonian rocks were deeply buried and covered with Carboniferous rocks, but that the earth and its rocks moved hugely, and any Carboniferous rock was eroded away, leaving ribs of tough Devonian stone across the land in the early Permian era. We really can’t be sure there were ever any Carboniferous rocks, but it is quite likely that they came and went, leaving no trace.

Later, the land all sank deep into a sea of some sort of cataclysm. In the Budawang ranges, the lowest layer of the Permian rocks is a conglomerate containing very large boulders, telling us that the first deposits in that part of the basin were laid down in a huge flood.

At Myrtle Beach, on the south coast of NSW, this conglomerate layer is missing, suggesting that the oldest Permian sediments there were laid down at a different time. It may have been a few years, more probably it was a few millennia—or even quite a few millennia. Geology never scurries.

Myrtle Beach, south coast of NSW. The sloping beds below are pointing to 1 o’clock,
and the hand (top left) spans a gap of about 100 million years in the geological record.

There is also a simpler sort of time gap, much harder to identify, called a disconformity. This happens when sediments stop being delivered for a while, but we can largely ignore these hiccups for the moment. We now have the basic background to understand a bit of slightly more detailed geological history. 

The laws and principles of geology

Nicolas Steno started it. Here is a modern version that conveys his thinking in the language we use today.

* Steno’s Law of Superposition says that in a sequence of strata, any stratum is younger than the sequence of strata on which it rests, and is older than the strata that rest upon it.

* Steno’s Law of Original Horizontality says that strata are deposited horizontally and then deformed to various attitudes later. That is, undisturbed true bedding planes are nearly horizontal, though we need to note here that cross-bedding is possible where sandhills or sandbanks are being formed.

* Steno’s Principle of Lateral Continuity: strata initially extend sideways in all directions. That is, every outcrop in which the edges of strata are exposed demands an explanation, and strata on two sides of a valley represent erosion of the rock between.

* Steno’s Principle of Cross-cutting Relationships: anything that cuts across layers post-dates them. This applies particularly to igneous intrusions such as dykes. Aside from Steno’s principles, geologists accept the following notions:

(1) an intruding rock is younger than the rock it intrudes into;

(2) a fault is younger than the rock which is faulted;

(3) any pieces of ‘foreign’ rock included within a rock must be older than the rock they are found in; and

(4) William Smith’s principle of fossil succession.

We will come to that in a moment, but geology was only possible because of James Hutton. He had made enough money from an ammonium chloride factory to be able to retire from work and study geology.

Hutton was an old friend of Joseph Black, the first scientist to distinguish heat from temperature, and also of James Watt (the steam engine maker), so it is no surprise to discover that Hutton assumed that all earth activity was due to what he called the earth’s ‘heat engine’. But most importantly, he said that “…The past history of our globe must be explained by what can be seen to be happening now”.

He emphasised the igneous origin of many rocks (unsurprisingly, given that he came from Edinburgh, where igneous rocks rear up all around the town). Unfortunately, the French Revolution was happening, so the public in Britain was less than enthusiastic about Hutton’s revolutionary notions. They were not only unready for his ideas, they were unwilling to accept them, but the scene was now set.

John Playfair was probably one of the few people to combine geometry with geography and geology. Trained in mathematics at a time when geology had not yet been invented, Playfair was necessarily largely self-taught. Like James Hutton, Playfair was exposed to the stimulating geology of Edinburgh, which would have assisted him in his work.

He also invented geomorphology, giving us ‘Playfair’s Law’, which states that rivers cut their own valleys. Then he gave us the modern concept of grade when he asserted that the angle of slope of each river shows an adjustment towards a balance between the velocity and discharge of water on one hand, and the amount of material carried on the other.

Playfair also made the work of Hutton more accessible when he published his Illustrations of the Huttonian Theory of the Earth in 1802. He explained the rock cycle of repeated weathering, erosion, deposition and solidification in simple terms: notice, with a modern eye, how he covers weathering, erosion, sedimentary rocks forming in the sea and uplift.

The series of changes which fossil bodies are destined to undergo, does not cease with their elevation above the level of the sea; it assumes, however, a new direction, and from the moment that they are raised to the surface, is constantly exerted in reducing them again under the dominion of the ocean. The solidity is now destroyed which was once acquired in the bowels of the earth; and as the bottom of the sea is the great laboratory where loose materials are mineralized and formed into stone, the atmosphere is the region where stones are decomposed, and again resolved into earth.
—John Playfair, Illustrations of the Huttonian Theory of the Earth, 1802, 109.

The idea of igneous rocks came later. Playfair’s ideas only gained wide acceptance after Charles Lyell added Playfair’s ideas into his Principles of Geology, but we have left out William Smith, an orphan who was set to work early as a surveyor for the new canals that were beginning to cross the British countryside, so industrialists could haul goods from place to place.
These canals required digging into the ground, and they had to cut tunnels through hillsides. This all gave Smith first-hand chances to observe and classify the many rock types as they are seen in fresh unweathered exposures. Most importantly, he noticed how strata were typified by fossils, and he pointed out that the same stratum could be identified at a considerable distance by the fossils it contained.

In 1816, Smith published his ideas, accompanied by a coloured geological map, and made the point that, given the law of superposition, the fossils in the strata gave us a view of the history of life on earth. Now the way was fully prepared, and Charles Lyell’s Principles of Geology could be released in the early 1830s, just in time for Charles Darwin to take them with him on the voyage of HMS Beagle. That meant he was prepared to unravel in full detail the reasons why life actually possessed a history on earth.

That is how science weaves itself into a web, but it also involves cycles.

Geological science is also science, and there are some principles of science, as well. I will get to those in part 3.

Sunday, 1 September 2019

What geologists think, part 1

A small note up-front: this is a sample from one of my coming attractions: completed or nearly ready works that don't suit my current publisher, and haven'y yet been sold.

* * * * * * * * * * * * * * * * * * * * * * * * *

Beach pebbles, Gerringong New South Wales.
In my closing-out process, I am getting well into Not Your Usual Rocks. Here's a small taste of what is to come in the series.

Every cliff, every rock face, every pebble, will carry a story of the past written on it—if you know how to read it.

The rules of thumb we use to read the rocks are scientific geology, but science is variable in its quality and in its actions. Think of a grassy mat, sitting in shallow sandy soil on sandstone. 

In the middle, there is less struggle for life, but out on the fringes, the struggle is intense, because it’s drier out there, with less soil. Yet, if one grass runner reaches across to some neighbouring soil, the whole species will advance.

Science works in a similar way. For most of the time, most of the scientists in any branch of science agree, about most things, just as the grass in the middle of the mat agrees that all is well. Out on the fringes, we find patches of dead and decaying science.

Even in the centre not all scientists agree all the time, because every now and then, somebody does a bit of tweaking. They adjust a few of the assumptions for some purposes. Once in a while, a scientist does the equivalent of there must/might be better soil out there, somewhere.

The more general a scientific rule-of-thumb is, the more scientists agree about it. But no rule is sacred: if somebody finds even one contradiction, people need to think, and toss out a part, or even all, of the rule.

Sometimes, the two models rest happily, side by side. If we are sending rockets to another planet, the 330-year-old physics of Isaac Newton is good enough, but for some parts of physics, we need the more modern insights of Albert Einstein.

These days, the tweaking seems to happen less often, but it always remains possible that one of the foundations, one of the basic assumptions of geology may need to be altered or even discarded. The standard propositions that guide geological science are also principles that explain why the world looks as it does. 

Hawkesbury sandstone cliff, North Head, Sydney.
 How much story can you see in this picture? I can see lots, but then I was trained by clever observers and I’ve been looking curiously at rocks for six decades—and I know the things that geologists agree about, things like the following principles work well, because they explain the weird shapes that the earth we live on can take.

How do we explain this, without geological science?

1. We can see where the world has changed.

The world does not abide forever, even if, in our short life spans, the world really is fairly permanent. An occasional volcanic eruption or a massive earthquake can make a difference to what we see. 

Floods can move huge amounts of sediment as mud, and the occasional collapse of a delicate eroded arch may be seen, once the erosion goes too far or in a flood, but that’s about it for changes in the human lifetime.

On a larger time scale, continents shift around, pushing and jostling. As they do, they shove the Swiss Alps, the Himalayas, the Andes and all the other mountainous parts of the world up into the sky. At the same time, weathering destroys the rocks and erosion carries the remnants down to lower reaches. Without rocks being pushed up, there would be no mountains left.

Tilts and folds, Mt Pilatus, Switzerland.
Sometimes, land sinks deep beneath the sea, and new material gets washed in and laid down on top of it. Later, some of those new underwater rocks may be shoved back up into the air. All geological-scale things are slow, and we know this because we can work out the dates of the rocks.

2. We can tell the age of rocks.

Our various dating methods can give slightly different results, because geochronology, the dating of rocks involves inexact measures. Sometimes the assigned date relies on inference or assumptions, like the cases where we find fossils that come from a species that only lasted a short while, so we say that when similar layers in two cliffs contain that index fossil, they are the same age.

There are a few potential traps. We may have misidentified one of the fossils, or we may be wrong about how long that species lived. The good news is that we keep finding new methods and new data, so that over time, the picture becomes clearer. The good news is that the adjustments are generally small, because the different methods all give a consistent picture.

At times, we may use the half-lives of radioactive minerals, or other measures: once again all of the methods give consistent results. The order of formation given by different methods is the same, and over time, we have got much better at putting precise year-counts, on things. Our planet formed around 4.6 billion years ago, though the sandstone I walk on most days is Triassic in age, and roughly 200 million years old, but the sandstone won’t last forever.

3. We can see that rocks break down.

Geologists know perfectly well that rocks don’t abide forever: they are by no means everlasting. Their minerals break down, mainly under the combined effects of water and air, and the rocks come apart under the mechanical effects caused by heat, cold, grinding rocks carried by rivers and glaciers, and even from sand-blasting in deserts when strong winds blow.

Then there are the biological influences on the rocks—and I don’t exclude my walking on sandstone from this. Tree roots grow into cracks in rocks and expand, splitting the rocks, while at the other end of the plant scale, some mosses can drill neat holes in quartz, one of the toughest of minerals.

An echidna, Tachyglossus aculeatus, North Head Sanctuary, Sydney, Australia, about 10 km from the centre of Sydney.
Burrowing animals from ants to echidnas drag grains of partly-weathered material to the surface where the grains are more exposed to sun, water and rain. On the surface, large grazing animals make pads. These are tracks along the sides of hills, pushing sediment down and providing a path for water to run off downhill when it rains, carrying surface sediment away, In bulk, the Earth abideth well, and nothing is ever lost—it just bobs up in a new hat.

4. Geology involves reusing old material

None of the material coming from rocks is ever wasted. Calcium from basalt will eventually be dissolved and carried to the sea, where corals, snails and other marine life will extract it and use it to make skeletons, shells or something else.

Later, these dead animals may fall down and over time, their shells become limestone. Sometimes, the shells just dissolve once more, and over time, the limestone dissolves and washed down to the sea. Sand becomes sandstone, mud becomes shale, and so on.

If rocks get buried deeply enough, they may be changed by heat and pressure, so sandstone becomes quartzite, limestone becomes marble, and shale becomes slate. If the rock is covered enough, it may end up as molten lava that spews out onto the surface of the earth again. Rocks aren’t all “just rocks”, because the world’s rocks have different origins.

5. Rocks come in three main types

You may have missed it, but in the last paragraph, I touched on the three different sorts of rock: the ones made from sediments, the ones shaped by heat and pressure, and the ones that were melted before they formed rocks.

Sedimentary rock: Triassic sandstone, Blue Mountains, west of Sydney.
Sedimentary rock forms when sediment (bits and pieces of almost any sort) falls to the bottom of a lake or sea (or sometimes the bottom of a vast sand dune). Later, it is buried and a complex combination of pressure, water washing through and maybe mild heat, turns it into a rock. Sedimentary rocks are the ones that sometimes contain fossils, though a few deformed fossils can be seen in slates, while many show up in marble.

Weathered granite, Freycinet Peninsula, Tasmania. Obviously granite, if you are trained!
Igneous rock is any sort of material that was once a liquid, because at high temperatures, all rocks will melt. Granite is laid down, far below the earth’s surface, and only shows when a whole load of other rock erodes and weathers away. Granite cools slowly enough for big mineral crystals to form. Basalt, on the other hand, is oozy stuff that flows and spreads. Some basalt comes out of volcanoes as lava, some gets out and flows across the land, making a flat sheet that cools fast, so the crystals are very tiny.

North Bondi, Sydney, contact metamorphism: a volcanic neck erupted through the sandstone here, changing it to quartzite.
Metamorphic rock (the name comes from Greek, and means changed shape) forms when another kind of rock is subjected to heat and/or pressure. Large metamorphic regions are usually formed by extreme heat and pressure, and this is called regional metamorphism.

When melted basalt flows over other rocks, or when a volcano pushes through other rocks, the heat may travel a few metres or tens of metres, producing contact metamorphism.

In short, there are very few inexplicables when it comes to looking at the rocks, because in the end, the rocks are attacked and wiped out. Still, you can tell when an inexplicable shows up, because the scientists start flapping their hands until they work out an explanation.

Partr 2 is about explaining