Christmas Bells

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Christmas Bells - Blandfordia nobilis

Tuesday, June 27, 2006

The Nature of what is underneath Robertson.

What is underneath Robertson? Rock, you might say, and you would be right. But it is perhaps not what you might expect.

The local mechanic in the village, the charming Peter Vaughan, has at his yard hundreds of core samples which were left over after some test drilling was done in the district. From memory, it was done by people from Wollongong University, but it could well have been Department of Mines, for all I know. Anyway, the important thing is that these core samples - each about 1 metre long, and about 45 mm in diameter, contain some basalt rock samples, then mostly the samples are of sandstone rock, and in some levels coal (but not much of it).

So, the core samples show that if you drill straight down from Robertson, you find a bit of basalt, and then you find lots and lots of sandstone. You can see this sandstone exposed, in places like Carrington Falls. That is the heavily eroded valley of the Kangaroo River. But you can read the geological history of the land there, better than just about anywhere else.

Regular readers will know that Robertson is a basalt area. But the basalt is only a cap, sitting on top of the sandstone which underlies the entire area.

If you look at the image at left, you will see Bell's Hill, one of the local basalt hills (about 2 Km, south from Robertson). It is sitting over the sandstone plateau. Just project the line of the sandstone plateau to the left, and the bit on top is the basalt cap, but, the sandstone is a continuous strata underneath. Kangaroo Valley is visible to the left, in the distance.

Bell's Hill can be clearly seen in the panoramic images of Robertson I showed last week.

This photo looks straight down into the history of the earth.

This is a view of Kangaroo Valley, taken from Jamberoo Mountain Road, near Vandenberg Road, about 1 Km from the Pie Shop corner. The photo above was taken from the same place.

Bell's Hill (in the photo above) is just out of frame, and only about 1 Km away from the clifflines of the Kangaroo Valley.

So, what you see here - these sandstone strata - lie underneath Robertson.

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