Road cuttings are often the geologist's best friend. Civil engineering projects such as a new road will reveal hidden structures in the landscape. But even then it can take a trained eye to spot the subtle variations in the strata. Not so here....
Multi-Coloured Rock Stop
You will find yourself looking at a spectacular road-cut showing alternating layers of black mafic gneiss and grey felsic gneiss cut across by steeper-dipping sheets of granite and pegmatite. Notice how the pink pegmatites "pinch and swell" into bulbous shapes. These indicate that the rocks into which they were intruded were at the time very hot and quite soft.
Throughout this area, known as the Laxford Front there are abundant sheets of pink granite and pegmatite, intruded about 1750 million years ago.
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Question to Answer: "Using the exact words given in the information board, how did the black dolerite and pink granite penetrate the grey gneiss?"
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