Craiglee is a rugged hill just over 500m high in the hinterland of the Galloway Hills. It is pathless terrain, with uneven ground, rocky outcrops, bog and dougalls in places. It is somewhere that you need to come to prepared for a day on the hill. This means walking boots, waterproofs, food, warm clothing, water and an ability ot navigate on and off the hill. That means without relying on a GPS. If the clag comes down up here, and you run out of battery power, you will need to use a compass and map to get you safely off the hill.
The co-ords take you to a place known as Sound Clint, which is a tall rock face on the slopes of the hill. The rock which Craiglee is made from is an igneous rock, namely Granodiorite, which was formed approximately 393 to 424 million years ago in the Devonian and Silurian Periods. It is an intrusive rock.
Intrusive rock forms within the crust from the crystallization of magma. As the magma pushes up from deep, it eventually slowly cools into a solid, and forms rock. An intrusive rock is any form of igneous rock that forms within the crust of the planet. Large areas of magma that solidify underground before they reach the surface are known as plutons, this area is part of the Loch Doon pluton, which extends from Loch Dee north to Loch Doon. If you look at a map, you can see this area, which takes in Craiglee, Craignaw, Dungeon Hill and Mullwarchar.
When the magma is ejected from the earths crust, such as during a volcanic eruption, the igneous rock is then known as extrusive rock.
So why are we here? We are here to look at Sound Clint, namely the area indicated by the image in this cache listing. Find the location of where Colin is stood, and then it is time to look closer.
On a recent excursion on Craiglee, or rather coming off the hill, we stopped at Sound Clint and remarked on the geology, that it turn stimulated me to find out more, and this we have this EarthCache.
We are here to learn about vesicles.
As the magma cooled, gases within it, expanded and formed a cavity, these cavities are known as vesicles, basically a bubble of gas, formed as the rock cooled and solidified. It is a cavity left by the gas. Vesicles are more common with abrupt changes of temperature and pressure; as gaseous escapes are linked to temperature and pressure which in turn control the vesicular texture, so can be seen more in extrusive rocks, as intrusive rocks as they cool do not allow for abrupt temperature or pressure changes, so lesser vesicles. Plutonic rock is formed deep underground and seldom contains dissolved gases, so reduced changes of vesicles, but what we have here, are some vesicles, not a lot, but they are here.
Amygdaloids are vesicles that have been filled in with a secondary mineral long after the rock cooled. Such secondary minerals are commonly white: quartz, calcite, or zeolite. (A secondary mineral is one that formed after the rock originally formed.)
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.
1. Please look at the vesicle indicated by the finger of Colin, how wide is it, how deep is it?
2. It is an amygdaloid, what is your rationale?
3.Looking at the face of Sound Clint, you will see some other vesicles, what shape are they?
4. How high is Sound Clint?