This Earth Cache is located in the Brisbane CBD along Adelaide Street.
Excavations in the Brisbane CBD have uncovered significant geological zones that underlie the city. Argillite, Greywacke and Phyllite are some of the rock uncovered during excavations.
Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found in Palaeozoic strata. The larger grains can be sand- to gravel-sized, and matrix materials generally constitute more than 15% of the rock by volume. The term "greywacke" can be confusing, since it can refer to either the immature (rock fragment) aspect of the rock or the fine-grained (clay) component of the rock.
The origin of greywacke was problematic until turbidity currents and turbidites were understood, since, according to the normal laws of sedimentation, gravel, sand and mud should not be laid down together. Geologists now attribute its formation to submarine avalanches or strong turbidity currents. These actions churn sediment and cause mixed-sediment slurries, in which the rocks may exhibit a variety of sedimentary features. Supporting the turbidity current origin theory is that deposits of greywacke are found on the edges of the continental shelves, at the bottoms of oceanic trenches, and at the bases of mountain formational areas. They also occur in association with black shales of deep sea origin.
Greywackes are mostly grey, brown, yellow or black, dull-colored sandy rocks which may occur in thick or thin beds along with shales and limestones.
Greywacke
** Please be mindful of the traffic at this location. Do not attempt to go the wall. Very limited parking. **
Questions
Q1 Describe the rock face on the other side of the road. What colours do you see here and how many layers do you count.
Q2 What difference in colour and texture is the top layer and the one along the bottom (not the retaining wall).
Q3 What direction does the cutting look to lean to?
Once you complete the EarthCache requirements you can post your find without delay, as per the EarthCache guidelines. You will also need to verify your find by sending me a message and provide your answers to the questions.
For a link to my profile, click here - Na'wal
Thanks for visiting this Earth Cache. Hope you enjoy the location.
Feel free to attach photos to your log (optional)
References ~ Wikipedia, excavation document by David Qualischefski