(An asterisk* indicates where the formation can be seen around Lismore)
Below is a draft version. We welcome any additions. "contact us".
(Quartz reef in ironstone at Lake Tooliorook. How did that get there???!)
Our story begins a while ago.......
4-5 Billion years ago - A mass of dust from exploded large stars (forming heavy elements), small stars (lighter elements) gathered to form our sun and earth. This settled to form a core, mantle, crust, water, and atmosphere.
Land masses drifted over the surface of the earth.
A link at the bottom of this page gives an animation of this.
Eventually the land, part of which is now Australia was located over south pole. (Some ancient soils (called cratons) still exists in western and southern Australia and is roughly where present day iron ore mining is happening). This was all part of “Gondwana”. The area of the south pole was not frozen at that stage.
500million years ago (mya) (Ordovician era) - rocks to the south of Ballarat formed a sediment. Later cracks formed in this rock which filled with seams of gold bearing quartz.
380 mya (Devonian era) - Granite plutons formed underground in an area which is now north from Lismore to Linton and Stawell.For the granite to cool slowly underground (to form its large crystals) there must have been 100m to 1000m of rocks above which has now eroded away.
Granite has formed Mt Kinross (Wallinduc), Mt Emu (north of Skipton), Mt Cole (Beaufort).
Browns Waterholes has cut a channel down through to the granite, and it is also exposed in the highway cutting near the cemetery turnoff.The granite of the area varies in texture and in colour from grey to pink to white.
(Granite in Browns Waterholes, north of Heriot St)
(There is no granite around Derrinallum, just young basalt over limestone and deeper sediments.)
150 mya (Jurassic) - Gondwana started to drift apart to form Africa, South America, Antarctica, India, and Australia. Parts of all of them share similar ancient soils, plants and animals. Kangaroo grass on some roadsides is also in many of these continents and probably was there when they formed Gondwana.
It may be that our local long necked tortoise started to evolve at about this time, and the yabbie started a bit earlier.
95 mya (Mid Cretaceous)- The area was uplifted above water level and much of the surface rock was washed away to form what is now the Otways and beyond. Dinasaurs were evolving and some remains are found in the rocks of the Otways.
20mya(Tertiary/ Pliocene) - Large mountain ranges eroded to form replacement sedimentary rocks and soils to cover again the granite and limestone.
Some are northwest of Lismore* and on the northeast shore of lake Tooliorook?.
This is possibly a “Pliocene Black Rock sandstone”. This or a similar rock extends around the the north of Lismore. Locally we call it the "boomerang ridge". It apparently extends underground and around the lakes as far as Leslie Manor.
(Pliocene Black rock sandstone, Lake Tooliorook)
This possibly was from the erosion of old mountain ranges to the north.
(Laterite at road cutting on Skipton Rd, 2.5 km north of Hamilton hwy)
At some stage the area under water was uplifted and supported plants and wildlife.
10mya (Miocene)- The area west and south of Lismore and east up to Rokewood was under a shallow sea and again limestone was deposited.This was called the "Otway basin".The sea probably reached to Lismore at that stage, then gradually receded.
The Limestone on the southern shore of Lake Tooliorook* and Struan dam* This can be quite thick. Another deeper band of limestone called “Gellibrand marl” runs at various depths under much of the surface from Lismore to the coast.
The limestone layer provides water for the Gellibrand River and Otway Water supply to Lismore.
(Limestone layer at Struan dam, Lower Darlington Rd)
Lava vents flowed over old valleys from Melbourne to Hamilton to form the present basalt clay plains* Also Mt Widderin, Mt Hamilton, Mt Vite Vite. This took millions of years.Lava flows to the east of Lismore to Cressy. This is older and different composition the basalt beyond the stony rises to the west of Derrinallum to Mortlake*
(basalt layer over limestone layer exposed on east side of Struan dam)
2mya - Lava flows to the west of Derrinallum to Mortlake. The stony rises flowed over this at a later stage. The Mount Emu Creek cut a channel through this. It can be seen where the Mt Emu Ck crosses the highway at Darlington*.
100,000 ya - The area was lush, with giant kangaroos, wombat and diprotodons roaming.
Fossil of diprotodon tooth was found on west shore of L. Corangamite.* Other fossils and tracks have been found in the sediments of other local lakes.
(Cast of Diprotonon fossil tooth found west side L.Corangamite 1967)
40,000ya - Aborigines settled in Australia, later moving south and leaving middens of freshwater mussel shells around the early (Lake Corangamite and Lake Rosine?) and later lakes*.Pollen and diatom remains in the lake beds indicate that the climate was still quite lush.
20,000ya - Mt Elephant erupted to form a scoria cone and later the lava flows of the stony rises for 10km to the north, west and south*. The stony rises lava flows from mt Widderin and Mt Elephant probably meet near Hannah's Rd.The climate went through a dry period, with long periods of dry lakes.
Research published in 2016 states that eruption of Mount Elephant can be put at 500,000 years ago, similar to Mt Widderin and Mt Rouse.
Aerial surveys show an ancient river valley, now covered by basalt, flowing from Skipton southwards past Camperdown.
(Basalt quarry west of Camperdown Rd, 2km south of Derrinallum)
The Mount Elephant scoria is described as “nepheline hawiites with phenocrysts of olivine and other crystals.”
The lava possibly blocked Salt Ck to form Lake Tooliorook*. Other lakes also formed in the district.
Recently, when lakes dried up the dust from their beds blew to form lunettes to the southwest of each lake. One is on the approach to Lake Tooliorook camping ground*, and to the southwest of Lake Gnarpurt*.
The dust storms of 1983, 2007 (and most summers) are part of this process.
To be continued.........
(Geological map of Lismore.)Q=quarternary, D=devonian, T=tertiary: v=volcanic, gd=granodiorite, pb=ferruginous sandTo download a free, later more detailed map click here
Rock profile under Lismore
Note that the town sits on granite. The only traces found of the older rocks originally over the granite are in the Gala gravel pit.
The cap to north of Lismore was a lake bed, and the limestone to south of Lismore was sea bed.
Lake Tooliorook rock profile
Derrinallum rock profile
note there is no granite. The stony rises sits on the plains basalt. This sits on the limestone sea bed, which sits on the older base rock of which there is no trace but which may be similar to the otways.
Oldest local rocks
550mya Cambrian - Gneiss and schist At shallow depth and creek crossings near Chatsworth/Wickliff/Willaura.
480mya Ordovician - Slate and quartz in mullock heaps dug looking for gold from Cape Clear to Bendigo.
440mya Silurian - Sandstone in creek crossing Woorndoo, sandstone hills Cape Clear to Ballarat
400mya Devonian - Granodiorite in creeks and cuttings from Lismore to Linton.
Links to other sites
Click here for a fun web site which shows how the cotinents have moved around the earth over time and how the sea level has changed. (To alter the time scale click on the (+) and (-) bottons then move the red slider.) (Monash University)
Click here for a similar site that also explains what the weather was like and what animals were about. (Wiley book publishers)
Click here for excellent map and description of geologic development of Australia. Click on its help button to see how to work it. (By Geoscience Australia).
Click here for a description of the local soil types with interesting maps and a description of how water travels through them. (P.Dalhaus, Ballarat University)