I've walked up here a couple of times recently and noticed there are quite a few Xenoliths in the rocks - I found a stone you should be able to observe from the pavement without getting in the way of people coming in and out of doorways.
"Xenolith" literally means "foreign rock" and gives an insight into the formation of igneous rocks a long time ago.
The tall buildings here made it difficult to get a GPS fix, you may find directions useful - you'll be stood with Niddry Street directly behind you, GZ is right at the end of a restuarant and before a kiltmaker. Use the photo below to see the stone we're looking at here.

1) There are two xenoliths in this stone- which one is at the top of the stone, the bigger or the smaller one?
2) Describe the larger xenolith (shape, size, colour) and why it stands out from the rest of the stone.
3) Why do you think the xenolith is there? Use the information below to help with your answer.
4) Take a photo of yourself at GZ, or an identifying item, being careful not to reveal any of the answers to the questions.
Please submit your answers via message though the Geocaching website or by sending me an email - there is no need to wait for a response before logging your find.
Xenoliths

Xenoliths, are foreign rock inclusions found within igneous rock formations, such as granite. Their formation begins deep within the Earth's crust, where molten magma slowly cools and solidifies to form granite. During this process, pockets of magma may intrude into existing rock formations, incorporating fragments of the surrounding rock into the cooling magma. These fragments, known as xenoliths, are often of different composition and texture compared to the surrounding granite. As the magma cools and crystallizes time, the xenoliths become trapped within the granite, preserving a snapshot of the geological history of the area. Studying xenoliths provides valuable insights into the complex processes occurring beneath the Earth's surface and aids in understanding the evolution of Earth's crust.
Xenoliths are usually visible. They have a different color and density than the surrounding igneous rock. Xenoliths can be as small as a grain of sand or as large as a football, and as long as several meters.