Include a picture of one or more of the crosses carved on the wall of the cave in your log, if you cannot find the crosses, improvise your photo at the mouth of the cave for your log.
YOUR CHOICE OF SITES TO VISIT,PHOTOGRAPH AND MATCH UP
Isolated pillars of sandstone probably arose through a contrast in the cementing by carbonate, whereby the softer, less well-cemented sandstone has been eroded away completely. Bedding features in the sandstone are well displayed.
The scallop-like fossil in this view is a Pecten, and it is in the Pabay Shale, of Jurassic age. Pectens are very common in the fossil record. There is also a small v-shaped bivalve, probably a small Pinna, at upper left.
This ridge of rock running out to seaward is a much eroded sill formed by igneous material intruded between beds of Jurassic sediment.
This is a large fossil bivalve. There are several specimens in the Pabay Shale, which is of Jurassic age.
The surface of this bed of Pabay Shale contains several belemnites.
These are the fossil skeletons of a squid-like marine creature that lived in Jurassic times. The longest one here is about four inches (10 centimetres) long.
The brown lumps are carbonate concretions which have formed in the Scalpay Sandstone, then been exposed by erosion and are themselves being weathered to a honeycomb surface. Some of them have split into two or more sections.
A Curved sill. The saucer shape of the igneous body on the beach is probably the result of the magma that formed it being intruded between curving beds in the crust of the Earth.
The ridges crossing the flat shoreline rocks are igneous dykes intruded long after their host rocks were formed.
View of cliffs with the Jurassic Scalpa Sandstone at the foot and the basalt columns of the Staffa Formation above. Sròn nam Boc means 'the buck's nose', and it is applied to the crest of the ridge here. There are also Toarcian black shales, Greensand and Cretaceous sediments, but these are not easy to pick out from sea level, and it requires a risky scramble to get close to them. No climbing required here for this cache.
Rock succession. The rocks at beach level and in the lower cliffs are Jurassic sandstones, but in this view the overlying basalt lava flows, some with well-developed prismatic jointing, are also also displayed. The contact between rocks which are around 180 million years old and the basalts of around 58 million years marks a considerable leap in Earth history.
This is a large fossil bivalve. There are several specimens in the Pabay Shale, which is of Jurassic age. This specimen is partly under the water of a small rock pool.
Dyke an igneous intrusion that cuts across the sedimentary deposits on the beach.
Cross-cutting Veins There are three veins on the surface of this pitchstone rock. A broad one runs from upper left of centre to lower right of centre. This is cut by a narrower vein running from lower left of centre towards the top right corner. Both of these veins are cut by a third one running straight across, half-way up this view. Thus it is possible to tell which is the oldest and which the youngest. This technique enables geologists to determine the relative of ages of rocks at all scales from tiny veins like these to large dykes which can continue for many miles.
Click here FOR THE ROUTE DESCRIPTION.
Click hereTO VIEW THE SNH FOSSIL CODE.
Click hereTO VIEW COMMON FOSSILS, ROCKS & MINERALS.
Click hereTO VIEW GEOLOGICAL FIELDWORK CODE.
Click here TO VIEW, Ancient Carved Crosses inside the Nuns cave,Carsaig arches footpath,Ross,Isle of Mull,Highlands,West. Photo+ info.
Click here Archaeological Notes.
FURTHER READING AND REFERENCE:
For more historical info: see: RCAHMS Argyll Volume 3 (Her Majesty's Stationery Office Edinburgh 1980) ISBN 0 11 491591 1
Click here For Interactive British Stratification Tables (OU).
Click here Geological Conservation Review Carsaig Bay.
Click here Marine Bivalve Shells of the british Isles .
Click here British Lower Jurassic stratigraphy
Click here Dykes and Sills Formation
Click hereTO VIEW GLOSSARY OF GEOLOGY