Castletown Limestone
The landscape here at Scarlett is one of the most varied and interesting on the Isle of Man. The most striking feature is the limestone rocks. This whole area has been quarried for centuries, first of all near to the sea, and more latterly, in the 19th century, in the huge quarry behind the visitors’ centre. Limestones in the South of the Island were formed, in the Carboniferous period, around 330 million years ago, when the Isle of Man lay thousands of miles south of here, near the equator.
Image source: Manxgeology.com/geological-map
When Limestones were formed the Isle of Man was positioned close to the equator with much of the Island submerged beneath a shallow, tropical sea. This sea was inhabited by organisms such as corals, crinoids (a type of brittle star), numerous shellfish, primitive sharks and algae. The algae would grow together as clumps of slime on the sea bed. The slime would accrete calcium carbonate and trap mud, building up a solid mound of limestone representing an early form of reef.
Limestone consists mainly of the minerals calcite and aragonite, two crystallization forms of limestone. Other minerals such as clay minerals, dolomite, quartz or gypsum can be present in varying proportions. If the dolomite component predominates, it is called dolomite stone. If the limestone has a relatively high proportion of clay minerals, it is called marl. Limestone can contain up to several percent organic substance and is called bituminous limestone.
Rock Folds
Image source: Geoexpro.com/folds-and-folding-part-i
A wave-like geologic structure that forms when rocks deform by bending instead of breaking under compressional stress. Anticlines are arch-shaped folds in which rock layers are upwardly convex. The oldest rock layers form the core of the fold, and outward from the core progressively younger rocks occur. The hinge is the point of maximum curvature in a fold. The limbs occur on either side of the fold hinge. The imaginary surface bisecting the limbs of the fold is called the axial surface. The axial surface is called the axial plane in cases where the fold is symmetrical and the lines containing the points of maximum curvature of the folded layers, or hinge lines, are coplanar.
Sources: Wikipedia.org/wiki/Limestone, Manxgeology.com/limestone, Geologypage.com/2015/12/geological-folds
In order to log a find against this EarthCache, you will need to visit GZ and then answer some questions and send your answers to me via my Geocaching profile or through the Messenger Centre facility.
1: In what geological era and how many million years ago was the Castletown Limestone formed?
2: At Station 1 you see a fold in the rock on the ground. Describe this fold in the rock according to the type of fold, color and dimension.
3: At Station 2, the layers of Castletown Limestone can be seen to the left of the stairs. What angle do these layers have?
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