Due to a popular movie, the Jurassic period is often associated with Dinosaurs. It is true these creatures roamed the lands during this period, however it is often forgotten that the name Jurassic actually refers to a geologic period from 145 million to 201 million years ago. The Jurassic period sat there right between the Triassic and Cretaceous periods.
In the Jurassic Period, the area we now call Bath was under shallow sea-water. Gradually, tiny grains of calcium carbonate rolling around on the sea floor began to pick up layers of lime, grow in size and compact together. Over the next 200 million years, pressure from mounting layers of sediment caused those grains to form limestone. It is this Bath Stone that the area is widely renowned for today.
Two distinctly separate types of rock layer combined to enable the engineers to build the tunnel not far from where you are standing when at GZ.
The bottom of these layers is the Midford Sands, formed during the Lower Jurassic period. .
Above this layer is Oolite Limestone which can be seen in the roof of the tunnel, formed during the Middle Jurassic period. This Oolite is structurally inferior than the relatively newer Oolite nearer the top of Combe Down Hill which is seen in much of the building in Bath and commonly referred to as Bath Stone (the actual name of this is found on the information board and will help you answer one of the questions below).
At GZ you will find an information board worth reading. The rail tunnel was built under this 170,000,000 year old hill. Read the board enhance your knowledge learned in the above narrative.
To log the cache you must send a message to me through the geocaching website answering the following questions and then log your find. If I see logs and haven't received the answers then your log may be deleted. You may also wish to include a photo of yourself with the information board in the photo, however ensure the answers can not be read from your photo.
- How many rock layers are there under Combe Down Hill?
- Who was the first land surveyor to record these rocks, and what year?
- What type of stone is usually known as Bath Stone?
- What type of clay was used by the Romans to wash clothes?
- Describe the stones either side of the paved path inside the tunnel.
- Describe why the tunnel was built at the depth is was and how it has structural integrity (consider the rock layers and shape).
FTF Honours go to Grumpy Old Duffer. Congratulations!
2TF Honours go to redsox_mark. Congratulations!
3TF Honours go to UK2. Congratulations and well done!