214 STRATIGEAPHICAL GEOLOGY 



correlations made by Professor Barrels the succession may be stated 

 as follows : n 



II f 7. Shales with Entomis and Posidonomya venusta. 



PP er "^Q. Limestone of Fresnaic with Bactrites and Tentaculites. 

 Middle 5. Calcareous shales of Pont Maillet. 



'4. Gritty slates with Spirifer hystericus and \Dalmanites 

 laciniatus. 



Lower - 



3. Limestones with Athyris undata. 

 2. Sandstone with Orthis Monnieri. 

 \. Quartzites and slates (Plougastel Beds). 



Of these groups only 1 to 3 are found in the Laval Basin, 

 and the lowest is much thinner than in the west. In the basin 

 of Angers the Plougastel Beds are absent and the series begins 

 with the equivalent of the Gahard sandstone ; the succeeding beds 

 being all limestones or calcareous shales, and evidently deposited 

 much farther from land than those of Western Brittany. 



In the basin of Ancenis, still farther south, this change from an 

 arenaceous to a calcareous facies seems still more marked, for the 

 lowest beds there are limestones and shales of Middle Devonian age, 

 but it is rather uncertain whether the absence of Lower Devonian 

 is due to non-deposition or to faulting. There can be no doubt, 

 however, that in passing from west to east we pass away from the 

 land-area which supplied the arenaceous material, and this applies 

 both to England and Brittany. 



In Normandy only the Lower Devonian comes into the 

 synclines, so that the facies of the Middle and Upper Devonian is 

 unknown. The thickness is not great, for as in the south the 

 Plougastel Beds are absent, and the lowest beds are hard sand- 

 stones with Orthis Monnieri, which represent the Gres de Gahard 

 and rest unconformably on Silurian or Ordovician. Other fossils 

 are rare. The sandstone is succeeded by slates with lenticular beds 

 of limestone which contain Athyris undata, Homalonotus Gervillei, 

 Phacops Potieri, Spirifer Rousseaui, and are clearly the equivalents 

 of the greywacke of Faou and of the Athyris undata limestones 

 of Anjou. The highest beds to be seen are brown mudstones with 

 Pleurodictyum. 



2. Spain 



Devonian strata have been recognised in many parts of Spain, 

 making it probable that nearly the whole of that country was 

 covered by the Devonian Sea. Moreover, although the facies is to 

 a large extent calcareous the fauna is similar to that of Northern 

 France. As an example of the Spanish succession I select that of 

 Asturia, which was described in detail by Professor C. Barrois in 

 1882 ; 12 this is as follows : 



