Welcome to Caistor Roman Town, also known as Venta Icenorum!
This is an EarthCache which means that there is nothing physical to find at this location. Instead, visit the two waypoints and answer the questions below. Please send your answers to me by email or via the Message Centre. Once you have sent your answers, you can log straight away – I will contact you if there are any issues.
Questions:
1. At waypoint 1, is the water clear or murky? In line with the geology of the area, why do you think this is?
2. At waypoint 2, head to the middle of the bridge and look at the river bed:
a. Locate the chalk on the river bed and describe its features (e.g. colour, shape and size).
b. Do you think there is more chalk located on the north side of the bridge or the south side?
c. Does the river bed at this location contain any other rock type? If so, why do you think this is the case?
3. At waypoint 2, please upload a photo of yourself or a personal item with the bridge.
Chalk:
Chalk is a soft, white, porous, sedimentary carbonate rock. Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle. The particles that form a sedimentary rock by accumulating are called sediment. Examples include limestone.
Chalk is a type of limestone which was formed due to the compression of plankton, around 100 million years ago. When the small marine organisms died, they floated to the sea bed and were compressed to form the rock that we see today. Chalk is composed mostly of tiny fragments of calcite shells or skeletons of plankton. It is also usually almost pure calcite, with around 2-4% of other minerals within its composition. Chalk can appear in large structures such as cliffs or as small stones, which are often used ornamentally.
Chalk Streams:
Chalk streams are rivers that rise from springs in landscapes with chalk bedrock. Chalk is permeable so the water percolates easily through the ground and as such, a chalk stream receives very little surface run-off. The water in the streams therefore tends to contain very little organic matter and sediment.
When the ground water flows through the chalk bedrock, it re-emerges lower down the slope in springs. The chalk therefore acts as a temporary reservoir by regulating the amount of water being supplied to the springs. This is why many chalk rivers have stable flow regimes that vary only slightly over time.
There are only 210 chalk streams in the world and Norfolk has 25 of them! The River Tas is one of these streams and it rises from a network of springs at Carleton Fen. The river here has been physically modified so that it is wider and deeper than it would have been in the Roman period. As such, “siltation” has become more of a problem which means that although the river sits along a chalk bed for the whole of its length, it has also become blocked with sands, gravels and clays in places.
This cache has been placed with the kind permission and in collaboration with the Norfolk Archaeological Trust.