Geological background
The Devonian (Frasnian) Portscatho Formation is dominantly composed of alternating grey or greenish grey, sandstones and mudstones (slates) along with less abundant siltstones. The Mylor Slate Formation is well developed around Carrick Roads and is dominated by dark grey slates with thin pale grey sandstones and siltstones. This rock unit is also Devonian (Famennian) in age. The Porthleven Breccia Member is included within the Mylor Slate Formation, but comprises angular fragments of a range of rock types included within mudstones. Locally igneous rocks (originally basaltic in composition, but altered during regional metamorphism to what are referred to in Cornwall as greenstones) occur in amongst the Devonian sediments. All of these Devonian rocks were folded and regionally metamorphosed during a major mountain building event known as the 
Variscan orogeny some 350-290 million years ago.
Subsequently large granite masses were emplaced into the Devonian rocks. Two large granite bodies occur within the catchment area of the Fal Estuary; the Carnmenellis Granite to the west and the St. Austell Granite to the east. The Carnmenellis Granite is roughly circular in outline and is predominantly composed of muscovite-biotite granite. To the east of the estuary is the St. Austell Granite. This granite is composed of three main textural and lithological varieties; the eastern part is largely composed of biotite granite, whilst the western part is composed of topaz granite and tourmaline granite. The tourmaline (or lithium-mica) granite is extensively altered to kaolinite. The topaz granites occur as well defined bodies within the St. Austell Granite. (SOURCE: HERE)
The Portscatho Formation is often folded in places. At this location you are looking for a axial plane (explained below) as in the adjacent picture.
Basic fold geometry and nomenclature
Fold hinge and limbs - If we consider a single folded surface (figure 1) the main elements of the geometry of the fold shape are firstly the hinge or closure, which is the zone of maximum curvature 
of the surface, and secondly the limbs, which are the areas between the hinges. If it is possible to define a line of maximum curvature, this line is called the hinge line. A single fold comprises a hinge and two limbs which enclose the hinge. In a series of folds, each limb is common to two adjacent folds. Depending on the actual shape of the fold, that is, on the way in which a surface changes curvature, the hinge may be very sharply defined and the limbs relatively straight (figure 1B), or the curvature may be more constant around the fold if it approaches a cylindrical shape (figure 1C). In a truly cylindrical fold, where the fold surface corresponds to part of the surface of a cylinder, neither hinge nor limb can be defined, but such examples are uncommon.
Fold axis and axial plane - In describing the attitude of a fold, it is useful to refer, not to the attitudes of both limbs, but to the imaginary plane which is equidistant from each limb and which bisects the angle between them. This plane is termed the axial plane and cuts the hinge zone of the fold along a line which is termed the fold axis (figure 2A). Provided that the limbs of a fold are sufficiently well defined, the determination of the orientation of axial plane and axis will give a precise description of the orientation of the fold. It must be remembered that these terms refer only to a single fold surface.
To validate your find in this EC:
Get to the coordinates and look for the axial plane. The pictures above will help you identify the feature but remember that it is a linear feature - you are looking for a line that clearly disrupts bedding (stratification). After you identify it, answer the following questions and send me the answers via e-mail or the geocaching message service. Please identify the cache.
1- What is the orientation of the axial plane?
2- How long is the axial plane on the outcrop?
3- Are the beds (strata), when they meet this axial plane, forming an "arrowhead" that points landwards or seawards?
PLEASE. No spoiler photos in the logs. Any logs with spoilers will be deleted without explanation.
Please beware of the tides. Slippery outcrop. Take care!
If you feel you have all the answers correct, please log your found but also send me the answers via e-mail so I can check them. If I don’t answer you it is because they are correct and you have another found.Please note that when you e-mail me or use the Geocaching message service, please supply the reference of the cache and please click on the “I want to send my e-mail address along with this message” so that when I reply to you the messages don’t go into e-mail heaven (or hell).
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