THE CAMBRIAN SYSTEM 101 



j a it hi 'i ue of Brittany, and there is consequently an absence of the 

 Upper Cambrian (Olenus fauna). Below the La Vega Beds and 

 apparently in conformable succession are the unfossiliferous Rivadeo 

 shit-, which may in part represent the Lower Cambrian, but Dr. 

 Barrois compared them with the Phyllades de St Lo which were 

 at that time classed as Cambrian. Further investigation is there- 

 fore required in this area where no base has yet been recognised. 



3. Belgium and the Ardennes 



In the Ardennes district there are four separate areas where 

 Cambrian rocks come to the surface, but only those of Rocroi and 

 of Stavelot are of any considerable size. 27 The one lies mostly in 

 France, forming a hilly plateau traversed by the deep ravine of the 

 Meuse between Deville and Fumay ; the other is on the borders of 

 Belgium and Germany around Spa and Stavelot The rocks have 

 the same fades in both areas ; they are much flexured and faulted, 

 but a definite succession has been made and the Belgian geologist* 

 group them in three stages as below : 



3. Salmian, consisting of slates and quartzo-phyllites in which I>ictyo- 



graptus has been found. 



2. Revinian, black slates and dark -grey quartzites. 

 1. Devillian, greenish and grey quartzites with bands of purple and 



green slate containing Oldhamia. 



The base is not exposed, and no fossils except Oldhamia radiata 

 and 0. antiqua have been found in the Devillian, which may be 

 of Middle or Upper Cambrian age ; while the Salmian may 

 certainly be correlated with the British Tremadoc Beds. 



In Belgium there is another area where a succession of Cambrian 

 rocks are found, i.e. in the valley of the Thyle south of Brussels. 

 Here the lowest beds resemble the Devillian and also contain 

 Oldhamia ; above them, near Mousty, M. Malaise has described a 

 set of black slaty shales with black limestones and bands of i licit. 

 and in the limestones he has found small Ostracoda which he refers 

 to Leperditia punctatissima and Primitia solvensi* (Lingula flag 

 species) ; these black beds are succeeded by quartzo-phyllades which 

 he also refers to the Lingula flags, and he correlates the Cambrian 

 of the Ardennes and of Brabant as follows : M 



Salmian 

 Revinian 



Ardennes. Brabant, 



Not recognised. 



\ Lower . 



Assize de Villers. 

 Assizo <K- Mousty. 

 Assize de Tubize. 

 Assize de Hlaumont. 



