Investigating Science 11–12 · Year 11

Logging the strata in a rock cutting

Module 1: Cause and Effect – Observing

PracticalMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

The idea

A rock face gives qualitative observations (colour, structures) and quantitative ones (bed thickness, grain size, dip), and the principle of superposition turns the measured log into an inferred sequence of events.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

traffic at road cuttings
falling rock from the face
sun exposure
uneven ground

Controls

never work on a live road shoulder; use only sites approved in the excursion plan
stay back from the base of the face and wear hard hats
no hammering of the face
hats, sunscreen and water

Note

Fieldwork: complete the school's excursion approval and a RiskAssess field risk assessment under NSW Department of Education procedures; any test reagents carried into the field fall under the Chemical Safety in Schools (CSIS) package, Section 1.

What you need

a safe exposure approved in the excursion plan (a cutting behind a barrier, a quarry viewing area or an outcrop in the school grounds), or scaled photographs of one for the classroom version
5 m tape and metre rule, grain-size comparison card with the Wentworth classes (clay below 0.004 mm, silt 0.004 to 0.0625 mm, sand 0.0625 to 2 mm, gravel above 2 mm)
hand lens (×10), compass-clinometer, camera with a scale bar, field notebook, hard hats and high-visibility vests

How to do it

Photograph the whole face with a scale bar and measure its total height.
Starting at the base, log each bed: thickness to the nearest centimetre, colour, grain-size class from the card, sorting, sedimentary structures (cross-beds, ripples, graded beds) and fossils.
Measure the dip of the bedding at three places.
Draw a graphic log to scale (1 : 20) with grain size on the horizontal axis.
Write separate lists of observations and inferences, then order the events using superposition and any cross-cutting features.
Swap logs with a second group that logged the same face and compare bed counts and thicknesses.

What you should see

The learner checks the log by comparing the summed bed thicknesses with the separately measured face height and reports the difference, and every bed carries a grain-size class rather than a description alone. Comparing two groups’ logs of one face shows which records agree (bed count, thickness, grain class) and which do not (colour words, “gritty”, “crumbly”), the benefit and drawback of quantitative and qualitative data the module asks about. The inferred sequence places the lowest bed as oldest unless structures such as graded beds or cross-bed tops show the sequence is overturned.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

A description is as good as a measurement for comparing rocks.
The top layer is always the youngest, whatever has happened to the rocks.
Layers form at a steady rate, so thickness gives age directly.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-8 INS11/12-1 INS11/12-3 INS11/12-4
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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