Welcome to Ilkley Moor! This cache is one of a series of caches that will take you on a tour of some of the many geological features that you can find at this scenic location.
Ilkley Moor
Ilkley Moor is an area of upland moorland, covering 676 hectares. Internationally, this type of moorland is rare, despite being relatively common in the North of England, and as a result has significant nature conservation interest. Mosaics of heather moorland, blanket bog, acid grassland and flowing streams make up the character of Ilkley Moor. Mixed with these are small stands of pine woodland, scattered trees, tarns and exposed rock faces.
Ilkley Moor is underlain by a succession of shale and course grained sandstones including the Addingham Edge Grit that forms the Cow and Calf rocks. The sand that forms these rocks was originally laid down on shifting sandbanks in a great river about 320 million years ago during the Carboniferous Period.
Deep burial caused the sand to harden into rock and subsequent earth movements and erosion brought the rock back to the surface again. By the end of the Ice Age, about 13,000 years ago, ice had scoured the moor and deposited the long low ridge of Lanshaw Delves, a glacial moraine. Since then peat has accumulated in sphagnum bogs.
Rock Carving
Sandstone is composed of sand-sized particles of rock which have been cemented together by minerals that were being transported under the ground through the buried sediments, the minerals coming out of solution to 'glue' the grains together, forming sandstone. The sandstone has not been subjected to the high pressures that other rocks, such as granite (which we talk about below), have been subjected to. As a result sandstone is, in general, more susceptible to weathering and erosion. We will go into more detail about this below.
Granite, an igneous rock, is formed from magma that cools very slowly over millions of years underground, and the resultant mineral crystals that form during cooling have followed a chronology of crystal growth which results in an intergrown texture which is much more resistant to weathering due to the lack of space between crystals, because there is no room for fluids, etc, to get in and so 'attack' the rock.
Granite crystals are interlocked as the minerals formed from the slow cooling of molten material. Sandstone does not have the same interlocking crystal system, as grains are 'glued' together when the sand is turned to sandstone rock. When this happens there are voids left throughout the rock, creating connecting spaces through which fluids can flow, so eroding the sandstone away. In sandstone, voids between particles are generally larger.
In general, the interlocking crystal system of granite does mean it is stronger than sandstones. However, this depends on where in the world you are. For example, granite rock in Jamaica weathers very quickly.
Logging your Find
In order to log your find, please send a message to my profile answering the below questions. The answers can be found by visiting the location, reading the above description, and taking observations in the field.
Look at the carving in the rock.
- What is depicted in the carving?
- Describe the difference in colour between the rock and carving. Why do you think this is?
- Explain what you think will happen to the carving over time, with reference to any prominent features in the carving.
- What are the benefits and disadvantages of carving in this sandstone rock rather than a harder rock (such as granite), both for practical purposes and longevity?
As Ilkley Moor is a stunning part of the world, you may optionally want to upload photos of your visit, of course I would love to see them! You can log your find immediately, but please send the answers within 24 hours. I will respond to your message as soon as I can. Logs where incomplete answers have been given, or where an email has not been received, may be deleted.