Leader was Noel Schleiger

Lichens.

A rapid survey of the granite tors and shelves on each side of the track revealed fresh lichen growth since the 2003 fires. Mostly the thalli were lime-green Rhizocarpon geographicum, an indicator of altitude world-wide. Most of the thalli were 1 cm diameter or less. As well there were oval to sub-circular yellow-green Xantho-parmelia. The perimeter was yellow-green whilst the centres were dark, some blown away to reveal a window. New lichen growth can occur in the window giving a "bull's-eye" effect. We were amazed to find one thallus measured 56 cm across, suggesting an age of 280 years. This thallus was facing easterly and must have escaped the 2003 fires and others before that.

Gnammas.

Gnammas are hollowed out cavities on the flat surfaces of granite tors and shelves. Rain water charged with tree litter can become acidic. If the water accumulates in a slight depression in the granite surface, a chemical reaction is set up with the rock matrix, which produces a powder when drying out. The winds can blow this clean. The next rain continues the process so that the wetting and drying over an extended period gradually deepens the cavity, holding more water. This is a gnamma.

Xenoliths.

Foreign rocks are harder to find in an I-type granite. The Buffalo Granite is a good example of an acid magma which has stoped up through the crust from the earth's mantle. It consists of coarse crystals of quartz, orthoclase felspar (pink), less plagioclase (white), black biotite mica and hornblende (black). The large crystals are produced by very slow cooling within the earth's surface, perhaps 2 km down.

As the granitic magma intruded the Ordovician sandstones and mudstones, the heat metamorphosed the sandstones and mudstones into hornfels (black). The rocks would be isolated and sink into the molten magma before the magma solidified into granite. The quartzite would change to quartz porphyry or into gneiss which is banded. The hornfels would change into felspar porphyry and then into microgranite and ultimately into granite, to be completely assimilated by the granite. If these xenoliths are elongated they could indicate flow structure. It is necessary to record the length, width and direction of each xenolith with a scale and prismatic compass as well as position with a GPS. The data so gained will be added to the data base of 1998 - formed for the centenary survey of Buffalo National Park. (Schleiger 1998).

Walk to the Sentinel

The afternoon walk to the sentinel revealed three more xenoliths, four aplite dykes, and 31 joints. This suggested late stage intrusives and jointing at the time of cooling. First was NE-SW and later NW-SE. in late Silurian to Middle Devonian times.

Eric McCrum

1: The Cathedral. Granite tors on Buffalo Plateau.
2: Lichen on granite.Mt Buffalo.