Welcome to McMaster Rocks - Limestone! Please read logging requirements as set out below in order to log a find. Please send me an email with the required information, and do not post any answers in your log. Pictures are always encouraged, however, be sure that they do not give away any of the answers! This earthcache brings you to a limestone wall, that is a part of the General Sciences Building.
📍 Overview
At first glance, this wall may look like simple building stone. But look closer — much closer — and you’ll find something remarkable:
This rock is filled with the remains of ancient life.
The limestone used here formed millions of years ago in a warm, shallow sea, where countless marine organisms lived, died, and settled onto the seafloor. Over time, their shells and skeletal fragments were compacted and cemented into solid rock.
Today, those remains are preserved as fossils, locked inside the stone — and now exposed on this wall.
But the story doesn’t end there…
This rock is still changing.
🌊 Part 1: Fossils — Evidence of an Ancient Sea
This limestone is known as fossiliferous (bioclastic) limestone, meaning it is made up of broken pieces of once-living organisms.
Common fossils you may observe here include:
- Shell fragments (brachiopods or bivalves)
- Crinoid stems (circular or ring-like pieces)
- Small, broken fossil debris mixed throughout the rock
These organisms lived in a marine environment, meaning this rock formed underwater — likely in a shallow tropical sea.
👉 The key idea:
This wall was once part of an ancient ocean floor.
💧 Part 2: Chemical Weathering — Rock in Slow Motion
Limestone is made mostly of calcite (calcium carbonate) — a mineral that reacts with weak acids.
Rainwater naturally becomes slightly acidic by absorbing carbon dioxide from the air, forming carbonic acid.
When this acidic water flows over limestone:
- It slowly dissolves the rock
- Creates rough textures and tiny pits
- Can expose fossils more clearly
- Produces staining and streaking patterns
👉 This process is called chemical weathering.
Even though it happens very slowly, you can clearly see its effects on this wall today.
🧠 Logging Tasks
In order to log this earthcache, please email me the answers to the following questions:
🔹 Question 1 – Fossil Identification (Observation + Interpretation)
Find two different fossil shapes in the limestone.
For each one:
- Describe its shape (e.g., round, curved, segmented, elongated)
- Suggest what type of organism it may represent (shell, crinoid, etc.)
🔹 Question 2 – Fossil Distribution (Higher Thinking)
Examine a section of the wall closely.
- Are the fossils:
- Evenly spread out, or
- Clustered in certain areas?
➡️ What does this suggest about how the sediment (and fossils) were deposited?
🔹 Question 3 – Rock Texture and Composition
Look closely at the stone surface.
- Is the rock made of:
- Large visible pieces,
- Fine material, or
- A mixture of both?
➡️ What does this tell you about the energy of the environment (calm vs. active water) where this rock formed?
🔹 Question 4 – Chemical Weathering Evidence
Find an area showing signs of weathering.
- Describe at least two visible features caused by weathering (e.g., roughness, pits, discoloration, streaks)
🔹 Question 5 – Process Explanation (Key Concept)
Explain how acidic rainwater changes limestone over time.
(Use your own words — keep it simple but clear.)
🔹 Question 6 – Fossils and Weathering Connection (Advanced)
How does chemical weathering help make fossils more visible in limestone?
🔹 MANDATORY - Take a photo of your GPS, or part of you with your favourite fossil clearly visible.
Congratulations to mmsm on the FTF!