Greetings fellow Foxies,
                                     Recently I climbed Yilliminning rock in the evening which is a great time to gain an understanding of its formation. There is a great story in the rock itself if you look closely.
Most continents in the world consist mainly of granite (a light coloured quartz and feldspar rich rock that crystallised out from molten magma (igneous rock). The continents are separated by black dense crystalline rock (a bit like dolerite used for road building) that underlies ocean floors.
 I suspect that the granite here formed up to two thousand million years ago (your ancestral line may have been bacteria then) when two geological plates were colliding. As one slowly slid underneath the other it was forced into deep molten rock of the mantle and gradually melted.
Being lighter, large domes of molten granite gradually forced their way upwards. They moved upwards through solid rock by “cauldron subsidence”. Intense heat from dome magma causes rock above to fracture and fall into the magma, creating a chamber that the magma moves into. Fractured rock from top and sides is often incorporated into the dome as partially melted xenoliths.
If they reach the surface, volcanoes spew out a fine grained granite like rock called andesite. However most times the domes stop two kilometers (km) or more below the land surface and gradually solidify into granite. You can tell that it cooled slowly because granite has large evenly spaced crystals.
 
Just think about it. As you stand on the top of Yilliminning Rock, you are 2 km below an ancient land surface.
 
The diagram on left shows ocean crust melting in the hot mantle after it has collided with and been forced underneath a continent. Molten material separates into dense black gabbro and lighter granite that rises towards the surface of the continent by cauldron subsidence.

​Like most of the large granite outcrops in the wheatbelt, Yilliminning Rock is an inselberg (steep sided dome of bedrock that has been exposed above the surface as surrounding land eroded away).
If you wander over the surface you can see the relatively uniform speckled pale crystalline granite.
But look carefully, and you will see more.
Yilliminning rock contains lots of roughly north-west/south-east corrugations that are easily seen at dusk as shadows define them. Simplistically, I think that these could be due to slight differences in rock composition from

• Magma intruding cracks in the cooling rock.
• Changes in crystal size and possibly mineral composition that occurred due to temperature and pressure changes as the granite slowly cooled while still molten.

The huge sheets of rock are geologically a very recent, and form in a process called exfoliation. Basically, granite is a very poor conductor of heat, and hot-cold temperature variations cause onion skin type cracks.
In winter, cracks expands as water in them freezes. Voila, a great home for Ornate Dragon Lizards (Ctenophorus ornatus). Eventually gravity and vibration/ pressure from earth movements (or more commonly humans) causes these sheets to break off and move downslope (or be crushed or carted away by humans!)
 The image below shows granite structure in a broken sheet

​Images below show rock sheet on the northern side of the rock. If you sit quietly, the dragon lizards (mini dragons really!) will come out. Watch them bobbing up and down to warn off intruders and running around on their tippy toes (evolved to help them avoid heat from hot rocks

Here are some great references
Geology of Granite
Overview of Granite Outcrops in Western Australia

Greetings fellow Foxies,
A knowledge of the underlying rocks and their history explains why the landscape and vegetation of Foxes Lair changes more over a short area than other places like Dryandra Yilliminning and Harrismith.
I guess that you need a good imagination to picture continental plates smashing together and separating again to repeatedly form and destroy supercontinents over hundreds of millions of years, and the associated earthquakes, volcanoes and mountain ranges that have formed and then weathered away.
Geology is very relevant!
 For example did you know that Darwin could be a suburb in Indonesia in 500 million years, and a visit to Bali will be a different experience, as it may be a new Mt Everest or a blob of melting rock underneath the encroaching Australasian plate?.
So here is a very simplified story!
In the wheatbelt we are on the Yilgarn Craton, a very old and stable slab of mainly granite (sandy soils) with greenstone strips (red soils, mineral fields). Since its formation (2,800 million years ago?) the craton has been stressed as it and then as part of Australia has collided with others to form supercontinents and then separated again at least five times.
These stresses caused faults in the bedrock and cracks that filled with magma from the earth’s mantle that we commonly see today as narrow lines of black rock (like dolerite) containing dark minerals that form reddish loam and clay soils (dykes).
About 2,400 million years ago a series of east/west dykes formed, with the biggest being the huge Binneringie Dyke (600 km long and up to 3km wide. The dyke aligns with the road from Quindanning to Williams and then the Williams Kondinin Road and on to Hyden and further east. Commonly driving on these main roads, I used to overestimate the amount of red soil in the district, but one soon comes into sandy soils on side roads
Narrogin and Foxes Lair sit right on this dyke that can be seen from the air as a discontinuous often double line of hills. The hills have resulted from intruded magma ‘cooking’ the surrounding rock making it more resistant to erosion, and stonier more resistant laterites formed on dolerites remaining as the surrounding landscape eroded away. The line is discontinuous because the extruded magma formed different rock types from quartz to ultramafic rock, and the dyke has since been cut by numerous younger faults and dykes.

Surrounding areas like Dryandra are mainly on granites crossed by smaller dolerite dykes (often as ridges such as on Candy Block).
Granite is actually an interesting rock. Here it formed by the collision of continental blocks. As one block slides under another it melts and huge “pools” of granite rise up and solidify as large domes like Yilliminning rock up to 2 kilometres below the surface of the plate above.
You can climb Yilliminning Rock now because over the hundreds of millions of years the overlying kilometres of bedrock have weathered and the soil washed away into the ocean.

Mind blowing stuff!
 Some light reading- Geology of Granite , Overview of Granite Outcrops
The image below shows my guesstimate of the Binneringie Dyke at Narrogin.

Last year, visiting American geologist Ray Grant noticed strange gravels that resembled South Australian fossils in the main street of Mukinbudin. The S.A. fossils called ‘clogs’ are calcified pupae cases of Leptopius species weevils (stone pigs).
Fossils have also been reported at Gracetown and the Pinnacles.
Leptopius larvae are grubs that feed on acacia roots in sand dunes before compressing an space in the soil and secreting liquid to make a case in which to pupate. After pupation the adult weevil makes a hole in the pupal case and digs its way to the surface. Over time the residual cases became cemented by a lime in the soil water.
Mukinbudin specimens are similar but chunkier and harder, and tend to have the exit hole at the end rather than the side.
I found a paper on fossilised Leptopius pupal cases in Weipa bauxite that look like those at Mukinbudin.

Greetings fellow foxies
I am sure that many of you have lain awake at night and pondered on this problem: "Why do salt lakes occur seemingly randomly along waterways, why are they round, and why do they often have dunes on one side and a steep slope on the other?.  Well ponder no more.

A good example is Taarblin Lake that is actually two interconnected lakes.

The answer is a bit complicated, but includes geology, earth movements, salt reserves in the subsoil, and long term climate variation.
Unlike most other countries, we do not have permeable sedimentary rocks under our soils. East of the Darling Fault the underlying rock is a huge slab of continental (mainly granitic) rock that makes an impermeable basement below the weathered layer. This has been fractured by faults and is crossed by lines of dark dolerite type rock that weathers to a tight red clay. These two redirect or block groundwater flow. Many Great Southern lakes started when groundwater has been forced to the surface where these structures intersect waterways.
In very dry periods winds would blow sediment out of the dry lake bed, causing it to become deeper, and producing dunes on the edge. When the lake was full, wind caused the water to swirl in a circular motion that cut away at the edges of the lake. Additionally, while a part of a supercontinent called Gondwana for hundreds of millions of years, Western Australia slowly eroded down to leave a relatively flat landscape.

There have been large climate fluctuations over the last million years or so that are associated with glaciation elsewhere in the world. In arid periods plants died and very strong north-west winds that created dunes on the south-east side of the lakes and reduced their volume. In wet periods swirling water in the lake cut into the western side of the lake causing it to move west to form a cliff.
Lake Taarblin was considerably larger when the climate was wetter 3000-4000 years ago, but the eastern side has since been infilled by dunes and interdunal salt pans.
When more water entered the soil than plants could use, salt was brought to the surface in groundwater causing salt patches. This is happening now after clearing bush for farm land, but it has also happened naturally in the past. Interestingly first Europeans in the district discovered that the existing lakes were mostly fresh, but did not fill as much as today.

You may have noticed that lakeside dunes are mostly sandy in the Western wheatbelt, but loamy with lime nodules in dryer areas. The reason for this is that lakes in the east tended to be dry and saline in arid periods with dunes created from the saline lake floor, whereas western lakes were full more often with sand washing in with the water.
You can tell the difference from the dunal vegetation. Acorn banksia (Banksia prionotes) and woody pear (Xylomelum angustifolium only occur on wind deposited sand.

However red morrel (Eucalyptus longicornis),  Kondinin blackbutt (E. kondininensis) and other salt tolerant eucalypts characterise the salty lakeside loams.

To complicate things a bit more, there is another factor affecting the location of salt lakes – major ground movement.
This is the story: When Australia finally separated from India on the west and Antarctica to the south, stress in the underlying basement rock caused two things to happen.

1. Great rivers used to flow south from as far north as Beacon in deep canyons to the south coast. The Antarctica separation caused the rise of a low east west ridge near the south coast called the Jarrahwood Axis that tilted much of southern WA down to the north and reversed the flow of these rivers. Resulting sluggish valleys with little slope filled up leaving a chain of lakes that only flow in a very wet year all the way to the Salt River past Quairading then the Avon to Perth.
2. The Salt River and other rivers like the Beaufort and rivers further north, were also large active rivers that flowed to the coast when India was gradually separating from WA. After the separation the Darling Range gradually rose upwards and blocked these rivers, causing them to back up as huge lakes that became the source for extensive sandplains to their south and east. A prime example is the Yenyenning lake system where the Salt River was diverted north to the Avon River.
These earth movements in conjunction with climate variation has resulted in large areas of aeolian soil in the wheatbelt. These include the Watheroo, Meckering/Cunderdin, and Corrigin/Quairading sandplains, and morrel blackbutt loams in the Lakes District.