Welcome to Trafalgar Square
As you explore this historic site, take a moment to look down at the beautiful Yorkstone paving beneath your feet. This natural stone holds clues to Earth’s ancient past, preserved in the form of ripple marks created by water movements hundreds of millions of years ago. This EarthCache will guide you in discovering these fascinating features and learning about the geology hidden in plain sight.
Formation of Yorkstone
Yorkstone is a fine-grained, sedimentary sandstone primarily quarried from the Pennine region of Yorkshire, England. Its formation dates back to the Carboniferous period, approximately 300 million years ago, when vast river systems deposited layers of sand and silt across extensive deltas and shallow marine environments. Over millions of years, these sediments were compacted and cemented by minerals such as silica and iron oxides, forming a dense and durable rock. The stone’s mineral composition and compact grain structure give it exceptional strength and resistance to weathering, making it a popular choice for paving, building, and heritage restoration.
One of the most striking geological features found in some Yorkstone slabs is the presence of preserved ripple marks. These ripples are sedimentary structures formed by the action of water or wind on loose sand, typically in shallow aquatic environments such as tidal flats, riverbeds, or coastal zones. Ripple marks develop as water currents or wave motions move across the surface of sand, creating rhythmic, undulating patterns. Once these ripple-marked surfaces are buried by subsequent layers of sediment and lithified over time, they can be preserved within the rock record as a fossilized representation of ancient hydrodynamic activity.
The study of ripple marks in Yorkstone provides valuable insight into the paleoenvironments in which the rock was formed. Symmetrical ripple marks typically indicate oscillating wave action, often associated with nearshore marine settings, while asymmetrical ripples suggest unidirectional current flow, such as that found in fluvial environments. By analyzing these patterns, geologists can reconstruct aspects of Earth's geological history, including past climates, water depths, and flow dynamics. In this way, Yorkstone serves not only as a durable building material but also as a natural archive of ancient environmental processes.
Yorkstone at Trafalgar Square.
Diagram of ripple types.
Tasks for This EarthCache
To log this EarthCache, visit the site and complete the following tasks. Send me your answers via Geocaching or email.
- Include "Yorkstone Ripples - Trafalgar Square - GCB7R72" on the first line of your message.
- Look closely at the ripples in the Yorkstone pavement. Are they symmetrical or asymmetrical? What does this suggest about the ancient water movement that formed them?
- Estimate the approximate size of the ripple marks. What is the spacing between the crests? How do the size and shape of the ripples indicate the strength of ancient water currents?
- Why do you think Yorkstone was selected for the paving at Trafalgar Square? List at least two properties of the stone that make it suitable for this purpose.
- In your log, attach a photo of yourself or a personal item with the Yorkstone ripples. (Note: photos predating the publication of this EarthCache are not accepted.)
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