Autumn Horse Chestnut Leaf Miners

Natural patterns caused by moth caterpillar infestation in leaves

These remarkable patterns on leaves of the Horse Chestnut tree (Aesculus hippocastanum) result from a combination of the natural changing of the leaf colour in autumn and the effects of infestation by tiny caterpillars of the Horse Chestnut Leaf Miner moth (Cameraria ohridella). This Spanish species has invaded Britain in recent years and is having a very noticeable impact on the appearance of this one type of tree but it does not seem to have an effect on the wood of the tree. I have noticed a decline in the numbers of conkers this year, which might have had something to do with the loss of photosynthetic capability in trees that have been bady affected, but could be attributed to a number of other causes as well.

The tiny caterpillars live in the shallow space between the upper and lower layers of the leaf, and eat away systematically between parallel veins, killing that area of the leaf and leaving narrow bands of dead tissue that cover the leaf in irregular stripes. These can be seen increasingly throughout the summer in infected leaves but in autumn, as the leaves change colour and naturally die back for the winter, the damage caused by the caterpillars becomes more pronounced. It looks almost as if some artist has been having fun decorating the foliage to celebrate Halloween.

Luminous Fungi

Fungus that causes decaying wood to glow in the dark

When you go out “trick or treating” this Halloween, not everything that glows in the dark will be a spectre, phantom, or ghost – or someone pretending to be one. By an incredible quirk of nature, one of the commonest of British fungi creates natural luminescence (Ramsbottom 1953). The Honey Tuft Fungus (Armillaria mellea) which grows on both living and decaying wood, has a vast hidden network of black fibres called hyphae that somehow or other make the wood glow in the dark.

This common fungus tends to grow most frequently on or near stumps of trees, with clusters of the fruiting bodies that can reach a metre across. The exact form that the Honey Tuft Fungus assumes can be extremely variable. It is the hidden parts of this fungus, the rhizomorph and mycelium, that are responsible for most of the luminous wood in Britain.

Luminous wood has been recognised since the time of Aristotle and Plato; and it may account for such phenomena as the burning bush that was not consumed by fire as seen by Moses in the Bible. Walter Raleigh in Elizabethan times is quoted as saying “Say to the Court it glowes and shines like rotten wood”. In 1667 Robert Boyle studied the luminescence of rotten wood – and that of decaying fish! However, the discovery of the fact that it was actually the infecting fungus in the rotten wood that was causing the luminescence was not established until the late 18th and early 19th centuries by people like Sowerby (1797), B. von Dershau (1822) and J F Heller (1843).

The fungus is known to widely infect wooden support structures in mines, and has been noted creeping across the floors of damp wine cellars. In the First World War soldiers placed small bits of luminous rotten wood on their gun sights and helmets to avoid collisions in the dark. In the Second World War the wood in a London timber yard is recorded as glowing so brightly on moonless nights that men on fire watch covered it with a tarpaulin in case it attracted enemy aircraft.

It makes me wonder whether many ghostly apparitions both indoors and out might be attributable to the hidden fibrous support networks of this common British fungus.


Ramsbottom, J 1953 Mushrooms and Toadstools, New Naturalist Series, Collins, London. Chapter 14 pp 154 -164, Sixth Impression 1972.

Fungus that causes decaying wood to glow in the dark

Fungus that causes decaying wood to glow in the dark

Ai Weiwei’s River Crabs

Ai Weiwei porcelain river crab installation He Xie at the Royal Academy of Arts in London

Three thousand porcelain river crabs make up an installation by Ai Weiwei at the Royal Academy of Arts in London. The exhibit is called “He Xie” which means river crabs but the word has the same Chinese pronunciation and spelling as the word for harmonious. Harmonious is internet slang in China for censorship.

Pea Stacks from Moulin Huet Bay

Silhouetted rocky outcrops of the Pea Stacks in Guernsey

The view seawards from Moulin Huet Bay in Guernsey has been immortalised on many an artist’s canvass, including Pierre Auguste Renoir whose work is highlighted by a sign at the bay itself. He painted the scene fifteen times during a month long stay in 1883. The jagged outcrops that feature in the picture are the Pea Stacks (which are sea stacks) carved by wave action into the Pea Stack Gneiss rock on the very tip of the Jerbourg Peninsula. This metamorphic rock differs in appearance and origin from the Icart Gneiss of Moulin Huet Bay and the Doyle Gneiss that makes up the main part of the peninsula.

Rocks at Moulin Huet Part 2

Contrasting rock textures at Moulin Huet Bay

The metamorphosed igneous rocks of Moulin Huet Bay in the Channel Island of Guernsey, the Icart Gneiss, are traversed by later intrusions of molten volcanic rock that filled spaces where fractures opened up in the gneiss. These intrusive rocks are sheet-like formations of varying extent and thickness, appearing on the weathering rock surface as narrow bands of contrasting colour and texture, and they are known as dykes. Dykes are igneous rocks that can be composed of different combinations of minerals, and they can also be metamorphosed later into yet more compositions. On Guernsey there are apparently six different types of basic (as opposed to acid) dyke and it is difficult to distinguish between these types when just observing in the field. According to the simple guide written by Pomerai and Robinson (1994) most of the dykes at Moulin Huet are made of dolerite, as shown in the examples illustrating this post. [There are also a couple of lamprophyre dykes which I will show in a separate post]. I am aware that this identification as dolerite may be an over simplification but will investigate further.

The photographs here show the contrasting textures and colours of the rocks, with the relatively fine-grained, smooth, and homogenous grey-green dolerite dykes within the coarse-grained Icart Gneiss and its large, squashed pink-orange feldspar crystals. In some instances, there are pieces of the Icart Gneiss within the dolerite, these having broken off the sides of the bedrock and become incorporated into the molten lava as the dyke was formed – these inclusions are called xenoliths.


De Pomerai, M. and Robinson A. 1994 The Rocks and Scenery of Guernsey, illustrated by Nicola Tomlins, Guernsey: La Société Guernsaise, ISBN 0 9518075 2 8.

Wave-cut Platforms at Marble Bay

Wave-cut platform at Marble Bay

Marble Bay, also known as Pied du Mur, lies on the east side of the Jerbourg peninsula on the south coast of the Channel Island of Guernsey. There is a major fault zone extending from Marble Bay across the peninsula to Petit Port; and this fault has given rise to an area of fractured Icart Gneiss with many small sheared quartz veins and one major quartz vein about 2-3 metres thick. The sea has worn away this zone of weak fractured rock to form the bay.

Evidence of the process of erosion can be seen in the smooth curved notches present at the base of the cliffs and also of some large outcrops of bedrock on the shore. These notches indicate how the rock is still being eroded to this day by the waves with their stone load. Visible beneath the pebbles on the beach are exposed areas of wave-cut rock platform that show the long-term effect of of this eating-away of the cliffs in relatively recent geological time.

The promontory on the northern side of the bay features a wide ledge at about 8 metres above sea level which is a remnant of an earlier wave-cut rock platform, created when the sea was at a much higher level than it is at present. The erosion of the bay can additionally be detected in the caves that have been sculpted out along minor faults in the cliffs, one of which has a collapsed roof (blow-hole) leading to the formation of a so-called geo on the outer surface of the cliff.


British Geological Survey Classical areas of British geology: Guernsey, Channel Islands Sheet, 1 (Solid and Drift) Scale 1:25,000. NERC, Crown Copyright 1986.

De Pomerai, M. and Robinson A. 1994 The Rocks and Scenery of Guernsey, illustrated by Nicola Tomlins, Guernsey: La Société Guernsaise, ISBN 0 9518075 2 8.

Roach, R. A., Topley, C. G., Brown, M., Bland, A. M. and D’Lemos, R. S. 1991. Outline and Guide to the Geology of Guernsey, Itinerary 9 – Jerbourg Peninsula, 87- 90. Guernsey Museum Monograph No. 3, Gloucestershire: Alan Sutton Publishing. ISBN 1 871560 02 0.

Rocks at Marble Bay 1

There is no marble at Marble Bay in the Channel Island of Guernsey! It looks as if there is but really there is none. The name is thought to be due to the massive vein of white quartz that crosses the beach. Equally, the name may have arisen from the phenomenon of encrusting bio-films of various types (algae, bacteria and lichens) that coat the rocks with vivid coloured patches of red, orange, yellow, and black.

The main bedrock in the bay is in fact Icart Gneiss with its large squashed pink-orange feldspar crystals (as found in the nearby Moulin Huet Bay on the other side of the Jerbourg Peninsula). This metamorphosed type of granite is riven by a single massive 2-3m thick vein of quartz in a fault zone that extends right across the peninsula so that the same vein reappears at Petit Port adjacent to Moulin Huet. Smaller branching veins of quartz also appear in the Icart Gneiss. What seems to be a large dolerite dyke with grey fine-grained texture and smooth surface additionally crosses the beach. The true appearance of each of the rock types is mainly masked by the bio-films and larger seaweeds attached to the rocks. Inter-tidally, however, some outcrops remain clear of growth, and the location of the wave-cut notch at the base of the cliffs is especially good for viewing the Icart Gneiss natural pattern and texture.


De Pomerai, M. and Robinson A. 1994 The Rocks and Scenery of Guernsey, illustrated by Nicola Tomlins, Guernsey: La Société Guernsaise, ISBN 0 9518075 2 8.