-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
Dornoch Cathedral, dedicated to the Conception of the Blessed Virgin Mary but locally known as St. Gilbert's Church, after Gilbert, Bishop of Caithness, its founder, succeeded Halkirk as the Church of the See of Caithness.
The Cathedral, now used as the parish church, was founded about 1223, but its date of completion is not known. It was burnt by the MacKays in 1570 and lay in ruins until partially restored for use as a parish church in the early 17th century. Further re-building and complete restoration in 1835 -37, cathedral is all rubble with ashlar dressings.
Rubblework consists of stones in which the adjoining sides are not required to be at right angles. It is used for rough masonry, as in foundations, backing, etc., and frequently consists of common field stone, roughly dressed; but whenever possible, quarried rubble should be used, as better bedding can thus be secured. Conglomerate and slate stones abound in many localities, and are cheap and durable. Stonework that is cut on four sides so that the adjoining sides will be at right angles to each other, is known as ashlar, no matter whether the face is dressed or not. All ashlar should have straight and horizontal bed joints, and the vertical joints should be kept plumb. Ashlar walls will present a poor appearance if not done in this manner.
Here both the rubble and the ashlar blocks are different types of sandstone. The ashlar is of a yellow sandstone, while the rubble is yellow, grey and red.
Sandstone is a type of rock made from sediment - a sedimentary rock. The sediment particles are clasts, or pieces, of minerals and fragments of rock, sandstone therefore is a clastic sedimentary rock. It is composed mostly of sand particles, which are of a medium size.
Sandstone has two different kinds of material in it besides the sediment particles: matrix and cement. Matrix is the fine-grained stuff (silt and clay size) that was in the sediment along with the sand whereas cement is the mineral matter, introduced later, that binds the sediment into rock.
Sandstone is usually almost all quartz, but other minerals—clays, hematite, ilmenite, feldspar amphibole and mica — and small rock fragments (lithics) as well as organic carbon (bitumen) add colour and character. The cement in sandstone is usually one of three materials: silica (chemically the same as quartz), calcium carbonate or iron oxide. These may infiltrate the matrix and bind it together, or they may fill the spaces where there is no matrix.Depending on the mix of matrix and cement, sandstone may have a wide range of colour from nearly white to nearly black, with grey, brown, red, pink and buff in between.
Red Sandstone consists predominantly of rocks of terrestrial origin, it does not generally contain marine fossils.
Sandstone forms where sand is laid down and buried. Usually this happens offshore from river deltas but desert dunes and beaches can leave sandstone beds aswell.When sand is deeply buried, the pressure of burial and slightly higher temperatures allow minerals to dissolve or deform and become mobile. The grains become more tightly knit together, and the sediments are squeezed into a smaller volume. This is the time when cementing material moves into the sediment, carried there by fluids charged with dissolved minerals. Oxidizing conditions lead to red colours from iron oxides, while reducing conditions lead to darker and greyer colours.
To claim this earthcache, please send the answers to the questions below to us by email / message centre - do not post in your online log.Your log may be deleted if this criteria is not met. Educational guidelines for Earthcaches are set by Geocaching.com and GeoSociety.org (Earthcache) and have to be adhered to.
1) On the south wall to the left of the doors you will find an ordnance survey cut mark and bolt, describe the appearance of the stone immediately above this and why do you think it is like this? Give reasons.
2) On the South East wall to the right of a small door, 7th block up, what is in this block and how do you think it got there?
3) On the East wall just under the left hand window, you will see 2 stones which are completely different to the grey, yellow and red sandstone. What colour are they, how do they feel compared to the sandstone and to which rock type group do you think they belong ? Give reasons and can you name this rock ? May need to google
4) The stones mentioned in Q3 above, one more can be found elsewhere in the cathedral walls, which wall? North, South, or West ?
While not compulsory, it is always good to see photos of your visit.
Cache "placed" with kind permission of The Reverend Susan Brown
Additional Hints
(No hints available.)