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Preferentially weathered intrusion

Here we can see evidence of preferential weathering! We talked about this a little bit when we were standing on top of Castle Hill. If you remember, the reason why Castle Hill and Magnetic Island can be seen today, even though they formed underground, is because all of the rocks around them eroded away while they remained. They remained because granite is very hardy, it does not erode or weather easily!

Here, a dyke or volcanic intrusion has blasted through the rock. That is the darker bit in the middle. It is similar to what we saw on The Strand. The bit that blasted through the rock has weathered faster than the bits on either side that were there before. Even though the middle part is newer, it has been eroded more as it is more susceptible to weathering! This is a result of the actual properties of the rock type. 

Geoscience Audio Tour around Townsville
  1. Castle Hill
  2. Dolerite Dyke Intruding into Granite Rock Wall
  3. Faulting in Granite
  4. Xenoliths in Granite
  5. Pallarenda Beach
  6. Pumice and Coal on the beach
  7. Weathered rocks
  8. Lava Flows
  9. Volcanic tuff
  10. Preferentially weathered intrusion
  11. Coarse volcanic tuff