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Museum Expeditions & Field Trips - 2010


PAS-DE-CALAIS - MARCH 2010

Coal was first discovered in France in 1660 near Boulogne-sur-Mer but the seams were small and their extraction difficult. Richer deposits were discovered further inland in 1723 that proved to form part of the extensive coal measures that stretch from the Kent coast, through northern France and southern Belgium, to the Ruhr coalfields of western Germany.

Dating from the Westphalian epoch of the Upper Carboniferous period, the Nord/Pas-de-Calais coalfield is 120km long and up to 16km wide in places.

The coal bearing strata in this part of France is almost 1200 metres below ground and are generally only 1 - 2 metres thick. This means that a significant amount of spoil is produced and conical heaps of this can be seen all over the region.

Reminiscent of the pyramids of Egypt, the twin 190 metres high spoil heaps that tower over the town of Loos-en-Gohelle, near Lens, are the highest in Europe.

Spoil heaps near Lens, France
CopyrightOliBac 2007

At the turn of the 20th century, these coalfields employed 85,000 miners and produced three quarters of all the coal mined in France. As with the east Kent coalfields, the last coalmine in the Nord/Pas-de-Calais region closed in 1990.


Geology of the area

The north-west section of the Nord/Pas-de-Calais region replicates the succession found in The Weald of Kent, i.e. Jurassic basement rocks covered by Gault Clay and Chalk from the Cretaceous, overlain by younger Tertiary deposits. Indeed, until the English Channel was formed around 8,500 years ago, the Weald Anticline was a single geological feature stretching from Kent in England to Artois in France.

The south-east section of the region forms part of the edge of the Paris sedimentary basin with mainly deposits from the Teriary.

The coal measure rocks date from about around 310 million years ago and comprise shales, siltstones and limestones, many of which contain fossils.

Neuropteris  Asterophyllites  Sigillaria  Sigillaria  Stigmaria


Notes for travellers


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THAILAND - JULY 2010

Pa La-u Waterfall

This waterfall in Prachuab Khiri Khan province, and close to the border with Burma, is one of the longest in Thailand. Part of the Kaeng Krachan national park, it has 15 steps rising over 500 metres, along a 2 km length. The waterfall is really divided into two, the Pa La-u Yai and the Pa La-u Noi, but appear as though they are one continuous waterfall.

The geology of this part of Thailand dates from the late Palaeozoic and comprises sandstone, siltstones and chert, underlain by shales and limestones dating from the Ordovician and Cambrian periods. The predominent rocks at Pa La-u are red sandstones dating from the Upper Carboniferous of around 300 million years ago. The red colouration being derived from iron staining, black crystals of which (iron pyrites) can be seen in the photomicrograph below.

Red Sandstone Iron Pyrites Crystals Geology of Thailand

This part of Thailand sits on the Phuket Terrane, south west of the Three Pagodas fault. Significant similarities with the geology of the Carnarvon Basin of Western Austalia is indicative that this terrane once formed part of the super continent of Gondwanaland which broke up in the late Palaeozoic/early Mesozoic.

Stone Museum of Geology extends its grateful thanks to Mr Tony Hills for the main photograph and specimen
that appear here and for contributing to the narrative.


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GRIMES GRAVES, NORFOLK - AUGUST/SEPTEMBER 2010

Grime's Graves is the only Neolithic flint mine open to visitors in Britain. A grassy pockmarked landscape of over 400 shafts, pits, quarries and spoil dumps, they were originally named Grim's Graves by the Anglo-Saxons after the pagan god Grim. Grims Graves = Grims Quarries.

Grimes Graves
CopyrightStone Museum of Geology
Flint, a variety of quartz silicate, is a hard and durable mineral that can be worked into a variety of forms and its surfaces will take a high polish. Small amounts of impurities commonly give a wide variety of colors to flint: red, pink, green, blue, yellow, gray, white, black.

It was the bottom layer of flint - lying below sands, clays and chalk - that was highly prized here as it was easily flaked, less flawed than flint from the other layers within the chalk, and had a lustrous deep black colour.

The mines extend over an area of some 96 acres and consist of at least 433 shafts dug into the chalk. The largest shafts are more than 40 feet deep and almost 40 feet in diameter at the surface. It has been calculated that more than 1,000 tonnes of chalk had to removed from the larger shafts, taking 20 people around five months, before the bottom layer of jet-black flint could be reached.

Once they had reached the flint, the miners dug lateral galleries outwards at the bottom, following the flint. The largest shafts yielded as much as 60 tons of flint nodules, which were brought to the surface and roughly worked into shape on site. The blank tools were then possibly traded elsewhere for final finishing. It is estimated that 60 tons of flint could have produced as many as 10,000 of the hand axes, which were the mines’ main product. Extrapolation across the site suggests that Grimes Graves may have produced around 16-18,000 tonnes of flint during its lifespan.

The geology of this area is unusual in that despite being many miles from a coastline, the upper chalk is overlain by sand dunes. These Breckland Deposits are derived from what are known as "cover sands". These are wind-blown deposits dating from the end of the Devonian Glaciation and produced by the cold, dry and windy conditions experienced during periglacial conditions The sand would have come from melt water from the Devonian ice sheet, the exposed bed of the North Sea and the weathering of till or boulder clay.

Sand Hard Chalk Soft Chalk White Flint Blue Flint Black Flint Iron Nodule

Grimes Graves
CopyrightStone Museum of Geology

Most of the mines have long since collapsed and this is what gives this 96 acre site its pckmarked, cratered appearance.

Two of the mine shafts have been fully excavated but only one - seen here - is open to the public and visitors can descend 30 feet by ladder to see the jet-black flint.

A small visitor centre/site shop is also available with static and audio visual displays illustrating the geology and history of this site.


Notes for travellers


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