186 STRATIGRAPHICAL GEOLOGY 



5. Belgium 



Silurian rocks of a normal character are only exposed in the 

 same valleys as disclose those of Ordovician age (see p. 145). The 

 succession according to the most recent researches of Professor 

 Malaise is as given below : 26 



Dark slates with Monograptus colonus and M. Nillssoni. 



Sandy slates with Man. vomerinus, Cyrtograptus Murchisoni, and Cardiola 



interrupta. 



Flagstones and shales with Man. bohemicus. 

 Black slates and quartzites with Climacograptus normalis. 

 Grey slates with Phacops Stokesi and Halysites. 



It will be noticed that nothing above the horizon of the Lower 

 Ludlow is exposed, but higher beds probably exist under the cover 

 of newer deposits. The Silurian, however, must thin out south- 

 wards, for no such beds occur in the Ardennes, where a series 

 known as the Gedinnien, and generally regarded as Lower Devonian, 

 rests unconformably on Cambrian rocks. 



6. France 



Silurian sediments occur in several parts of France, but 

 generally present a shaly facies with small developments of lime- 

 stone and are not rich in fossils. The most complete sequence of 

 zones yet recorded is that of the west of Brittany (Crozon 

 peninsula), where M. Kerforne has been able to recognise the 

 succession of graptolite zones given in the table below. 27 



West, East. 



Shales with Bolbozoe. 



" wifch Monograptus c lo ? us ? White Limestone of Erbray. 



and Orthoceras in nodules. 



,, with Mon. Salweyi. \ Black limestone of Briasse with 



,. with Mon. colonus. / Mon. colonus and M. vomerinus. 



1 Shales with layers of calcareo- 



, , with Mon. Flemingi. siliceous nodules, Cardiola inter- 



,, with M. riccartonensis. | rupta, and species of Panenka, 



) Dualina, etc. 



Shales with Cyrtoqraptus gein- 



Wlth Cyrtograptus. tvdanus. 



. ,, T..T Cherts with Radiolaria and shales 

 " wlth 



,, with Rastrites Linnaei. Sandstones without fossils. 



In the central and eastern parts of Brittany, as well as in 

 Mayenne and Anjcu, a similar set of beds is found, though there 

 are some lithological differences, and the graptolite zones have not 

 yet been worked out. The two areas are compared above. 



