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BRITISH. Coal-measures of South Wales, with underclays inclosing Stigmaria. FOREIGN. Coal-field of Saarbruck, with Archegosaurus. BRITISH. Mountain limestone of Wales and South of England. FOREIGN. Mountain limestone of Belgium. BRITISH. Yellow sandstone of Dura Den, with Holoptychius, etc. FOREIGN. Clymenien-kalk and Cypridinen-schiefer of Germany.
Sometimes they are soft clay; sometimes clay mixed with a certain portion of sand; and sometimes they contain such a large proportion of silicious matters that they become hard, flinty rock, which many of you know under the name of gannister. But all underclays agree in two points: they are all unstratified.
Sometimes, however, it is a soft clay, at others it is mixed with sand, but whatever the composition of the underclays may be, they always agree in being unstratified. They also agree in this respect that the peculiar fossils known as stigmariae abound in them, and in some cases to such an extent that the clay is one thickly-matted mass of the filamentous rootlets of these fossils.
The peat bog is a great mass of vegetable matter, which is every year growing thicker and thicker; and underneath it there is almost always a bed of thin clay, in look very much like the underclays, and this thin clay is penetrated by the rootlets of the moss forming the peat, exactly the same way as the underclays of the coal measures are penetrated by the stigmaria and its rootlets.
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