The Terrain Bituminifere becomes Carboniferous

Because of the historical use of coal in northwest Europe and its identification with a particular sequence of strata, the deposits and their associated strata were first formally named as the Terrain Bituminifere by the Belgian geologist Jean Baptiste Julien d'Omalius d'Halloy (1783-187$) in 1808. D'Halloy came from a rich aristocratic background and his interests in geology were stimulated by contact with the likes of Cuvier, Brongniart, Lamarck and Faujas de Saint Fond in Paris. He had a special interest in the coalmining region of Belgium and northern France and became Governor of the Province of Namur in 1814. Applying the stratigraphic principles of succession of strata identified by their characteristic fossils described by Cuvier and Brongniart, he produced an outline geological map of France, Belgium and parts of Germany and Switzerland in 1822.

D'Halloy's Terrain Bituminifere included the coal seams and related shales and sandstones as the upper part and the thick succession of limestones beneath them. This continental sequence of strata was similar to that mapped out by Smith in England. Here the overall name Great Coal Measures included an upper sequence of coal deposits and related strata and a lower sequence of sandstones, which are in places hard, gritty rocks. Their resistance to weathering and erosion has resulted in their surface outcrop as small, craggy hills and ridges beloved by climbers. The rock has been quarried for centuries as a building stone and more especially as mill stones, so much so that the strata were called the Millstone Grits.

Below the Millstone Grits lie thick limestones similar to those found on the continent. In England these were called the Metalliferrous or Mountain Limestones, because they typically form the hilly landscapes of much of the north of England and in places were rich in mineral deposits. A central line of limestone hills of this age separates the west and east of the north of England. It runs from Derbyshire and the famous ancient mining area of the Peak District north to Northumberland and into the southeast of Scotland around Berwick-upon-Tweed. And in Ireland much of the centre of the country is underlain by limestones of similar age.

Such limestones form very particular landscapes because of their geological structure and chemical composition. Rainwater soaks down through natural cracks in the rocks (called joints) so that there is little or no surface drainage on upland limestone landscapes. The calcium carbonate minerals of the limestone can be dissolved by slightly acidic rainwater to form bare fretted and fissured surfaces (called grykes in the north of England), with underground drainage systems of interconnected caves and passages. Such topographical surfaces are known as karst landscapes, a name derived from the Slovenian word 'kras', because they are particularly well developed in the limestones along the eastern border of the Adriatic.

Smith's stratigraphy and naming of strata were very much based on old vernacular and regional practice, largely derived from quarrymen's terminology. One of the first more formal and academic attempts to regularise the nomenclature was produced by Conybeare and Phillips in their 1822 book Outlines of the Geology of England and Wales.

As they wrote, 'the class of rocks thus constituted will contain not only the great coal-deposit itself, but those of limestone and sandstone also on which it reposes ... the epithet Carboniferous is of obvious application to this series'. At this time they included in the Carboniferous System a thick succession of sandstones known as the Old Red Sandstone, which occurs below the Mountain Limestone. Conybeare and Phillips thought that this Carboniferous System was distinct from both Werner's Flötz-Schichten and Transition Series, although, if anything, they considered it to be more allied to the latter than the former. The anglicised name Carboniferous has since become an internationally recognised system of strata and period of Earth time, but, as we shall see, without the Old Red Sandstone. The strata represent the Carboniferous Period of geological time, which we now know lasted from 354 to 290 million years ago.

However, as we shall also see (p. 323), North American geologists recognise two separate systems, an upper Pennsylvanian for the Coal Measures and the lower Mississippian for the Mountain Limestones. The fossil content of the strata had long been a subject of debate, especially with regard to the true nature and formation of fossils.

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