THK OKDOVICIAN SYSTKM 14i"> 



tract in Thuiingia are the only exposed areas of this system 

 between the extreme west of Europe and Bohemia. In Belgium 

 it is probable that Ordovician rocks form a continuous sub- 

 terranean outcrop, running for some distance from west to east 

 beneath the Cretaceous deposits south of Ostende and Brussels, but 

 they are only exposed in two or three valleys where the rivers have 

 cut down to them through the superincumbent strata. 28 



One of these tracts is round the highest tributaries of the river 

 Senne, south of Brussels ; another i.s at the head of the Dyle valley, 

 east of Nivelles ; and a third forms a long band north of Namur, 

 from Qembloux on the west to near Huy on the Mouse. The 

 rocks are much compressed, cleaved into slates, and folded into 

 steep-sided anticlines and synclines so that only a general succession 

 has been made out by the discovery of fossils at certain localities. 

 Thus in Brabant the Llanvirn and Arenig faunas have not yet 

 been detected ; in Namur a Llanvirn horizon has been found, but 

 the Arenig does not seem to be exposed. 



The lowest beds near Huy are black satiny slates yielding 

 Mglina binodosa and Didymograptus Murchisoni. Near Oxhe to 

 the west are black micaceous grits and slates containing Homa- 

 lonotus bisukatus, Trinucleus favus, and Orthis redux (probably 

 Llandilo), while at Fosse a Bala fauna has been found in gritty 

 slates with bands of felspathic sandstone ; the fossils including 

 Trinucleus seticornis and Calymene incerta. The same fossils with 

 Orthis Actonice have been found near Gembloux. 



4. Bohemia 



In the Bohemian basin, the position of which is shown on 

 Stanford's map of Central Europe, the Ordovician succession is 

 fairly complete and has a total thickness of about 3000 feet. It 

 is wholly comprised in the Stage D of Barrande, who indicated his 

 systems by letters without giving them special names (see Fig. 45). 

 His sequence is as follows : 



D 5. Grey and green shales with Ampyx Portlocki, Aynostiis tardut. 



Sphasrexochus latens, and Dicellograptus anceps. 

 D 4. Sandy micaceous shales, with species of Trinucleus, JSglina, 



Calymene, and Cheirurus. 



D 3. Black shales with Asaphus nobilis and Trinucleus Goldfussi. 

 D 2. Hard grits and shales with Asaphus ingens, Placoparia grandis, 



Acidaspis Buchi, etc. 

 D 1, g. Black shales with Placoparia Zippei, Barrandea crassa, Ogygiu 



desiderata, Redonia, and Didymograpli. 



Below the last beds and dividing them from the Upper Cambrian 



L 



