The classification of sedimentary rocks

There are basically two ways of classifying sedimentary rocks, either by how they originated or their composition. The latter takes into account such matters as whether they contain primarily coarse-textured sands or fine clays, or whether they have a high carbon content due to being composed largely or entirely of plant or animal matter. However, it is generally more convenient to combine the two methods into a single classification, as below:

Mechanical Formation

This group comprises rocks that have been formed after material has been moved in fragments from one or several places to another (by the action of wind, water, ice or gravity), where it has become consolidated either by pressure from later deposits, or by cementation, or both. The original material may have been very fine in nature, such as river-borne silt, or much coarser, such as rounded or angular pebbles or rock fragments.

The material that enables fragments to cement together may be a solution containing minerals of various kinds, such that sandstones may contain quartz, calcium carbonate or iron, the proportions of these determining its colour.

Very fine material will form clays or mudstones, less fine deposits lead to grits forming, and much coarser material results in a conglomerate or brecchia (in the former the pebbles are rounded, whereas they are angular in the latter).

Terms used to distinguish rocks by the size of their particles are Argillaceous (e.g. clay, mudstone, shale); Arenaceous (e.g. sandstone, grit); and Rudaceous (e.g. brecchia, conglomerate, boulder clay).

Organic Formation

These rocks were created from the remains of once living organisms which built up over very long periods of time. These can be further classified according to the nature of the plants or animals that comprised the deposits.

Calcareous rocks (chalks and limestones) consist mainly of calcium carbonate, formed from the skeletons of marine organisms, and are distinguished by the size and nature of the particles that comprise them. The finest particles are seen in pure white chalk. Limestone is more varied, including crinoidal, coral, oolitic and shelly, the terms denoting the type of primitive organism that is mainly represented in its formation. Fossils of much larger organisms are often found embedded in limestone.

Ferruginous is a term that denotes the presence of iron, usually from the precipitation of hydrated iron oxide in the water of ancient lakes and marshes. Decomposing vegetable matter formed the basis of ironstone and “bog iron-ore”.

Siliceous rocks can be formed from the remains of sponges and minute organisms such as diatoms (single-celled plants rich in silica). These include nodules of chert and flint found in other rocks, and beds of diatomite.

Carbonaceous rocks are formed from plant accumulations and are high in carbon content. Depending on the age of the deposits and the pressure they have been put under, they can take the form of peat, lignite or coal.

Chemically Formed

These come about from the precipitation or evaporation of solutions of salts. All water that falls as rain will acquire salt in some form as it runs across the surface or finds its way underground, and these salts are often partially or totally released before the water cycle is completed. Rock formation can occur when sufficient salts accumulate in the same place. Five types of chemical formation of rock types can be distinguished.

Carbonates.  Stalactites and stalagmites in limestone caves, or travertine around hot springs, are examples of carbonate deposition. Dolomite is a chemically formed compound of calcium and magnesium carbonate.

Sulphates. Hydrated calcium sulphate, in the form of gypsum or alabaster, is formed by evaporation in inland drainage basins.

Chlorides. These produce rock-salt, either on the surface or at depth.

Silicates. As well as flint and chert (mentioned above), sinter is a silicate rock, formed around the vents of hot springs.

Ironstones. Most iron ores have accumulated from chemical precipitation within sediments, although some are the result of igneous activity.

Sedimentary rocks are typically laid down in strata of varying thicknesses, and the process can continue at the same place for extremely long periods of time (millions of years in some cases). It is sometimes possible, for example, to detect annual depositions made by ancient rivers, and use these to determine the age of a particular formation.

© John Welford

Welcome to Stalin World!

Grutas Park is a sculpture park in woodlands deep in the Lithuanian countryside. It is otherwise known as Stalin World, as though it were Lithuania’s answer to Disney World. Perhaps it is.

The main feature of the park is the collection of dozens of statues and busts of former Communist leaders, including Lenin, Stalin, Karl Marx and the founders of the Communist regime that ruled Lithuania when it was part of the Soviet Union before 1990.

Grutas Park was the brainchild of Viliumas Malinauskas, who was at various times a heavyweight wrestling champion, a Soviet-era soldier and the manager of a collective farm. After the fall of Communism he made a fortune from mushroom farming, and it was this money that led him to create Stalin World.

In 1998 he bought many of the statues and busts that now grace the park when these came up for auction having been removed from public display in various towns and cities. Some of these were enormous lumps of granite or bronze whereas others were relatively small. Many had been damaged when being toppled from their previous places of honour.

Malinauskas had no wish to venerate these people – many of whom had been responsible for the death of thousands of people, but to remind visitors of the history of the Soviet Union and how terrible it had been.

To this end, Malinauskas acquired other features of the Soviet system, such as watchtowers from which Soviet-era military music blares, and other reminders of the “gulag” system of camps for political imprisonment. The closest one gets to a Disney World experience is the short train ride one can take in a cattle wagon – ushered on board by uniformed guards – to a reconstructed prison camp surrounded by barbed wire.

After opening Grutas Park in 2001, Viliumas Malinauskas reminded visitors that it was better to see something once than hear about it ten times.

© John Welford

A few facts about atoms

Everybody knows that all matter is composed of atoms, but there some facts about atoms that almost boggle the mind!

For example, we all know that atoms are extremely small, but did you know that you could fit two billion atoms into the dot on top of each letter “i” in “billion”?

An atom consists of a nucleus, containing protons and neutrons, and electrons that whizz in orbit round the nucleus. There are as many electrons as there are protons in the nucleus.

However, what is not generally appreciated is that an atom consists mainly of empty space! If you could imagine an atom that was the size of a sports stadium, such as a Premiership football ground, then the electrons would be whizzing round the upper tiers of the stands and the nucleus would be a pea in the centre circle!

In other words, all matter is an illusion – everything that exists does so thanks to the energy contained in atoms. The actual matter in the atoms is almost non-existent.

© John Welford

How the Pacific Ocean got its name

Why is the Pacific Ocean so named? It was thanks to the Portuguese explorer Ferdinand Magellan, who sailed across it in 1520. His voyage down the eastern side of South America had been beset by storms and so, when he eventually found a passage to the west (through what is now known as the Strait of Magellan) he was greatly impressed by the calm sea he found on the other side.

The Spanish word “pacifico” means peaceful, and so it seemed to be an appropriate name to give this newly-discovered ocean. Of course, no ocean is without its bad weather, although the Atlantic does experience more storms than the Pacific. However, Magellan’s original impression was what he marked on his map and the name has stuck!

What Magellan did not appreciate was that the Pacific, at 166 million square kilometres, was twice the size of the Atlantic Ocean and the world’s deepest, at up to 4000 metres. The Pacific Ocean is actually larger than all the world’s land surfaces put together.

© John Welford

That, which, who

The use of the correct relative pronoun is one that used to be extremely important – if you wanted to speak and write correct English – but it has tended to excite less wrath from the pedants, if used incorrectly, in recent years. 

We are talking here about “that”, “which” and “who/whom”. In general terms, “that” should be used to refer to persons, animals and things, “which” to animals and things, and “who/whom” to persons. 

The basic rule is that “that” should be used to define the meaning or intention of the preceding word or phrase, as in “the book that I put on the shelf was a novel by Dickens”, whereas “which” would be used when the identifying information has already been supplied, as in “The novel by Dickens, which I put on the shelf, was far too long for me.” 

The use of “which” implies that you are referring to a specific item as opposed to another one, but this is not universal – “that” is often used in such a context. 

You can use “that” for persons when any member of a defined group is being referred to, and “who” when it is a particular person. Examples here might be: “People that live in glass houses shouldn’t throw stones” and “Bert, who lives in a glass house, threw a stone.” In British English, it is common to use “who” in preference to “that” when there is uncertainty, but Americans tend to prefer “that”. 

It has to be said that the use of these relative pronouns is dying out in some quarters, and if omitting one does not change the meaning of a sentence, then there is nothing wrong in doing so. However, there are occasions when confusion can be avoided by including one. 

Consider this example: “Mr Jones said yesterday some shares fell rapidly”. This could mean either that he said this yesterday or that the shares fell yesterday. The ambiguity can be avoided very easily by placing “that” either before or after “yesterday”. 

In the interest of not using more words than necessary to make one’s meaning clear, omitting that/which/who should be encouraged – but only when the meaning really is clear. 

As to using “that” or “which”, it depends on how precise you want to be. A general principle of modern grammar should be that a difference that makes no difference is not a difference worth too much bother!

© John Welford

Trial by combat

Back in 2002 a man in Suffolk (England) named Leon Humphreys came up with an interesting idea for settling his dispute with the DVLA (Driver and Vehicle Licensing Agency), who accused him of not notifying them when he took his 125cc motorcycle off the road and did not re-licence it.

This is an offence, and the DVLA took him to court so that his local magistrates could levy the appropriate fine. However, Mr Humphreys objected that this was a flagrant breach of his human rights and that he would settle the matter as his ancestors would have done, namely according to the medieval rules of Trial by Combat.

Back in Norman times it was believed that the victor in a judicial combat had God on his side and must therefore be in the right.

Mr Humphreys suggested that the DVLA should put up a candidate to fight him, and he offered that the weapons in question could be samurai swords, Gurkha knives or blacksmiths’ hammers. However, he did also point out that the fight would be to the death.

Not surprisingly, Mr Humphreys did not get his way. The magistrates suggested that, if he was correct in his claim that trial by combat was still on the statute book, he would need to produce the statute in question. Unless or until he did so, he would be required to pay a fine of £200 plus £100 costs.

© John Welford

Evolution is not "only a theory"

People who try to discredit the theory of evolution, preferring instead to rely on the Book of Genesis, will often say: “But it’s only a theory”. The implication is that it is unreliable and unproven and thus no more worthy of trust than the creationist view that they espouse.

However, what they are doing is misunderstanding what the word “theory” means. To them, something that is a theory is, by definition, “theoretical”. It is a back of the envelope idea, something thought up as an explanation that is no more than a thought and without any firm evidence to back it up. Another word meaning the same thing would be “hypothesis”.

That is indeed one meaning of “theory” but it is not the only meaning. To a scientist, a theory is a set of ideas that constitutes an explanation of how something works. It is the next stage beyond the hypothesis because it incorporates the evidence that any reasonable person would accept. It is the generally accepted account of the phenomenon in question, incorporating the laws and principles that govern what is known and observed.

There are many theories of the latter kind. The theory of gravity is one such, in that it is an explanation of how large masses exert attractive forces on smaller masses. Another is the heliocentric theory that describes how the sun sits at the centre of the solar system and the planets move round it in their orbits.

Neither of these theories can be described as unproven hypotheses, although this might well have been the case some centuries ago. When Galileo advanced the heliocentric theory of Copernicus he was thought to be a dangerous radical whose thinking was disputed because it challenged the teaching of the Church.

The theory of evolution has also been challenged because it is thought in some circles to be contrary to religious teaching. The “only a theory” jibe is therefore thrown at it just as it was at Galileo’s theory.

However, just as the heliocentric theory has moved from the “hypothesis” meaning of the word to that of “accepted explanation”, so has the theory of evolution. The evidence for evolution is so overwhelming that it has long moved beyond being a hypothesis, although this was not the case when Charles Darwin first proposed it. It is now a theory that is accepted as fact in the same way that the heliocentric theory or the theory of gravity is accepted as fact.

To say “only a theory” implies that there is something better than a theory, and that if evolution was worth its salt it would be this something else. However, outside the world of mathematics there is nothing better. Absolute proof of anything is impossible unless the terms are defined so rigorously as to be make proof inevitable, as happens with mathematical statements and formulae. In the real world there are plenty of accepted facts, but they are encased in what are conventionally called theories. They are proven for all practical purposes and are therefore completely reliable. There is nothing more factual and reliable that a well-formulated theory, in the non-hypothesis sense, and evolution is one such.

© John Welford