154 GEOGNOSY AND GEOLOGY. 
subordinate beds of bituminous and anthracite coal. Argillaceous 
spherosiderite is found in considerable quantity. 
c. The Coal Formation proper. This is of great importance, as 
containing the true coal measures. Stone coal is indeed a subordinate, 
but yet a very prominent member. The principal mass is formed by 
conglomerates and carboniferous sandstones: of the former granitic and 
silicious conglomerates are the most important; of the latter, clay, marl, 
and quartz sandstones. Accompanying and subordinate masses are: 
limestone, marl, loam, marl clay, and potter’s clay, which are generally 
very bituminous, as also a grey slate clay, bituminous shale, drawing slate, 
and various modifications of coal. The thickness of this group varies 
sonsiderably, rarely however exceeding about 900 feet. The strata are 
‘rather horizontal than otherwise, although there are sometimes very great 
rregularities of position. The coarser conglomerates generally occupy the 
lower levels; the finer, the higher. A similar relation occurs between 
anthracite and bituminous coal; the former occupying the lower, and the 
latter the higher measures. The coal beds are generally only a few feet 
thick. The thickest known are those of Fimini (33 to 40 feet), and those 
of Dudley in England (33 feet). 
The cleavages of the coal are generally distinct, and cut each other at 
ight angles. The roof and floor of the bed generally consist of clay shale. 
Nodular masses of arsenical and iron pyrites, argillaceous carbonate of iron 
or spherosiderite, galena, zincblende, are sometimes collected in larger or 
smaller quantity. The occurrence of native mercury, amalgam, cinnabar, 
and horn quicksilver in coal measures, is exceedingly remarkable: these 
bodies concentrate in nests and are thus found in loam. Organic remains 
are met with in extraordinary abundance, being principally confined, 
however, to plants: animal forms are much rarer (mostly fresh water 
mollusca): fishes are nearly wanting. Such remains are generally in 
excellent preservation, especially when they lie in the very fine shales. 
In these the finest nervures of the leaves are sometimes retained. Coal 
itself is entirely composed of transformed vegetable matter, as is abundantly 
shown by microscopic and other investigations. Springs abound in the 
carboniferous system, particularly those containing iron and _ salts of 
sulphuric acid. The true stone coal group is very extensively distributed : 
it occurs of great extent in Great Britain, Belgium, in the vicinity of Aix 
la Chapelle and Eschweiler, about Saarbrtick and in the trans-Rhenish 
Palatinate ; on the borders of the Hartz in less quantity, more abundantly 
in Thuringia; also in Saxony, Moravia, and Silesia; in extensive districts 
in France, some portions of Spain, Portugal, North America, China, Japan, 
and New Holland. 
One of the most considerable coal basins is that of the Palatinate, which 
is about forty-four miles long, and from seven to thirteen miles broad. It 
rests nonconformably upon the transition slate rocks, while it is covered by 
Vosges sandstone and alluvium. PI. 46, fig. 8, is a section of this field : 
K indicates the coal strata, V the Vosges sandstone, and A the alluvium, 
This field is often broken through by various porphyries, causing a 
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