Siccar Point Field Excursion Preview

Sedimentary structures in the Silurian greywackes

In the field, examine the grey vertical beds in detail. You are looking for way-up criteria - features that tell you which was the original top and bottom. You might see grading - variation in grain size from top to bottom, and ripples - laminations produced by current flow. It can be quite difficult - you need to search! More below...

In the field look closely at the hard and soft bands. In each case you are looking for:

• Grain size: can you estimate the size of the largest grains in millmetres?

  If the grains are large enough to see (with a hand-lens) look for:

• Sorting: are the grains all the same size or is there a complete range of sizes?

• Angularity: are the grains angular or rounded or somwhere in between?

• Composition: are the grains made of quartz or fragments of rock or...?