The striped and layered rocks that underlie the promontory at Cape Tribulation look like sedimentary strata. They were just that at one time in the past but they have been altered and partly metamorphosed into metasedimentary rocks. They belong to a group known as the Hodkingson Formation and are the result of transformations brought about as two tectonic plates of the earth’s crust collided, with one plate then sliding under the other (subduction), generating tremendous heat and pressure that altered existing sedimentary rocks, promoted magma movements below the crust (leading to intrusive igneous rocks), and stimulated surface volcanic activity (making extrusive igneous rocks).
I am overwhelmed by the beauty of the Emily Young sculptures that are periodically exhibited in London locations for all to appreciate. Not only is the working of the stone exquisite but the selection of the stone for the work itself is amazing. As an amateur geologist I am fascinated by the range of colours, patterns, and textures naturally occurring in rocks, and to see them used to such great advantage is a privilege. I discovered an exhibition of Emily Young’s sculpted heads in the Southwood Garden attached to St James’ Church near Piccadilly on my last visit to London. They will be on display until January 2018. These pictures show aspects of a sculpted head called Veltha which is created in brecciated onyx, and it is displayed by courtesy of Bowman Sculpture.
Once upon a time the ancient palace at Knossos on the island of Crete was made of smooth white blocks of gypsum with polished surfaces that gleamed in the sunlight. The effect of weathering over the centuries has stripped away the surface of the building blocks and created rough textures and patterns of sharp edged furrows where acid rain has dissolved the stone as it runs over and down the masonry. The gypsum blocks mimic a phenomenon called rillenkarren found on a larger scale in limestone landscapes all over the world. These erosion patterns in the landscape are known as karst topography. I previously photographed an example of karst topography with rillenkarren in the Queensland outback in Australia near the old mining town of Chillagoe.
Apologies for the quality of these pictures taken way back in 2009 with my first digital camera. I just came across the images as I was sorting my photo collection. I took them on a holiday to Rethymnon on the island of Crete in the Mediterranean. At the time, I thought the strange patterns in the stone walls of the old Venetian fortress were part of the rocks themselves. Locally the bedrock is described as crystalline limestone. Looking at the pattern and texture now, I am not so certain. It looks more like something that has been caused by the weathering process. I am thinking that maybe over the centuries since the construction of the wall, the limestone has dissolved in rain water and the calcium has recrystallized in this way between the large and small rocks that make up the wall. This has in a way reinforced the wall by further binding the elements together. I don’t know whether the walls were originally built as dry stone or whether they incorporated mortar. The crystal formation seems to be acting as a mortar now.
I have seen something similar to this phenomenon on my beloved Rhossili Beach on the Gower Peninsula in South Wales. I will fish out some photos for comparison.
The rocks at Dog’s Bay in Connemara, Ireland, are part of the Galway Batholith. In particular they are composed of the Errisbeg Townland Granite riven by faults and many dikes containing other younger intrusive igneous rocks. The juxtaposition of the different rock types is a phenomenon marked by contrasting, colours, textures, and patterns. The whole rocky terrain has been levelled off and smoothed by ice sheets and reflects many glaciation features.
Feely, M. Leake, B.E., Baxter, S. Hunt, J. and Mohr, P. A Geological Guide to the Granites of the Galway Batholith, Connemara, western Ireland.Geological Survey of Ireland, 2006.
The stark landscape of The Burren in County Clare, Ireland, comprises fields of Carboniferous Limestone rock pavement with sparse and specialised vegetation divided by walls of precariously balanced rocks. Moss and lichens cling to the limestone boulders and bent thorn trees miraculously survive with their roots among the stones.