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690 STRATIGRAPHICAL GEOLOGY. — [Boox VI. 
the two countries agree. The remaining four étages answer to the 
English and Welsh Upper Silurian groups—the highest stage of all (H) 
indicating by its organic remains the approach of the Devonian system. 
Small though the area of the Silurian basin of Bohemia is (for it 
measures only 100 miles in extreme length by 44 miles in its greatest — 
breadth), it has proved extraordinarily rich in organic remains. M. Bar- 
rande has named and described several thousand species from that basin 
alone, the greater number being peculiar toit. Some aspects of its organic 
facies are truly remarkable. One of these is the extraordinary variety 
and abundance of its straight and curved cephalopods. M. Barrande has 
determined 18 genera and two subgenera, comprising in all no fewer 
than 1127 distinct species. ‘The genus Orthoceras alone contains 554 
species, and Cyrtoceras has 330.1. Of the trilobites, which appear in great 
numbers and in every stage of growth, the same indefatigable explorer 
has detected as many as 42 distinct genera, comprising 350 species; 
the most prolific genus being Bronteus, which includes 46 species entirely 
confined to the 3rd fauna or Upper Silurian. Acidaspis has 40 species, of 
which six occur in the 2nd and 34 in the 3rd fauna. -Proétus also numbers 
40 species, which all belong to the 3rd fauna, save two found in the 2nd. 
Other less prolific but still abundant genera are Dalmanites, Phacops, and 
Illenus. The 2nd fauna, or Lower Silurian series, contains in all 32 genera 
and 127 species of trilobites, while the 3rd fauna, or Upper Silurian 
series, contains 17 genera and 205 species, so that generic types are 
more abundant in the earlier and specific varieties in the later rocks.? 
France and Belgium.—The researches principally of Gogsselet have 
demonstrated that a considerable part of the strata grouped by Dumont 
in his “ terrain rhénan,” and generally supposed to be of Devonian age, 
must be relegated to the Lower Silurian series. He shows that, though 
almost concealed by younger formations, the Silurian rocks that are laid 
bare at the bottom of the valleys of Brabant can be paralleled in a 
general way as under : 
Schistes de Fosse; psammites and lustrous shales with nodules and even 
beds of limestone, containing most of the fossils of the group below, with 
the addition of Sphwrexochus nirus, and Halysites catenularia. 
Schistes de Gembloux ; pyritous black and greenish shales, which at Grand- 
Manil, in the valley of the Orneau, have yielded upwards of 50 species of 
fossils, including Calymene incerta, Trinucleus setiformis, Ienus Bow- 
mannt, Bellerophon bilobatus, Strophomena rhomboidalis, Orthis testudinaria, 
O. vespertilio, O. calligramma, O. Actonix, Graptolithus priodon, Climaco- 
\ graptus scalaris. 
Schistes bigarrés d’Oisquerq; variegated flagstones and shales, sometimes 
black and graphitic. 
Schistes aimantiferes de Tubize ; green, sometimes bluish and blackish rocks, 
comprising shales with magnetite and pyrite, and shales passing into slate 
and into quartzite. 
Quartzites de Blammont ; whitish and greenish quartzites becoming pink by 
weathering.’ 
Caradoc. 
Llandeilo. 
The Silurian rocks of Belgium comprise several contemporaneously 
erupted masses of porphyrite and of diabase, as well as beds of porphyroid, 
arkose, and eurite. | 
Silurian rocks have been detected in many parts of the old Paleozoic 
1 Syst. Silur. ii. suppt. p. 266, 1877. 
? Op. cit. i. suppt. “ Trilobites,” 1871, 
* Gosselet, “ Esquisse Géologique du Nord de la Trance,” p. 84. Mourlon, “ Géol. 
de la Belgique,” p, 40. Malaise, “ Mém. Couronn, Acad. Roy, Belgique,” 1873. 
