London Bridge EarthCache

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). Most limestone is composed of skeletal fragments of marine organisms such as coral, forams and molluscs.

Limestone makes up about 10% of the total volume of all sedimentary rocks. The solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock.

Limestone has numerous uses: as a building material, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, and as a chemical feedstock.

The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778.

London Bridge

The limestone of London Bridge Arch began to form when sediment and coral remains were deposited on an ocean floor 420 million years ago. It was then subjected to intense pressure. Over time the ocean receded and erosion shaped the landscape.

The arch was formed by water slowly leaching through the limestone, enlarging cracks until a passage became big enough for Burra Creek to pass through. It reached its present size about 20,000 years ago.

The arch was first recorded by Europeans in 1823 when explorer Captain Mark Currie was directed to the arch by an Aboriginal guide. Currie described it as ‘a natural bridge of one perfect Saxon arch, under which the water passed’.

• Do not rock climb on the arch or enter the caves—they are extremely fragile.

• Keep to the tracks and protect this special environment.

• Googong Foreshore is a wildlife refuge so please leave your pets at home.

• Take your rubbish home—there are no bins.

• Use the toilets provided at the car parks.

• Swimming and camping are not permitted

Questions 

To claim this Earchcache, answer the following questions:

1. If you look at the cave walls on the left and right, you will note that the horizontal limestone layers can be clearly seen. Now look up at the roof of the cave. Which way are the layers of the limestone facing?

2. How do you suppose this occurred?

3. (Optional) Post a picture of yourself at London Bridge.

UPDATE: Monkeys are all grown up, and I don't check in as often as I should. Feel Free to log your find.

With the publishing of this cache, C+2M will have earned our Platinum Level Earthcache Master