144 STKATIGEAPHICAL GEOLOGY 



Ordovician by the occurrence of fossils ; this is the Gorran quartzite 

 near Mevagissey, in which Calymene Tristani has been found and 

 which may therefore represent a part of the Gres de May. 

 Following this quartzite in what is believed to be descending order 

 are the following divisions : 26 



Veryan Beds, bluish shales with thin beds of limestone and of chert with 



Radiolaria. 



Portscatho Bed?, bluish slates and fine gritty flags. 

 Falmouth Beds, green and grey slates with layers of sandstone. 

 Mylor Series, banded slates with alternating layers of fine siliceous grit. 



The base is not exposed and no fossils have been found in any 

 of these beds, so that their age is quite uncertain, and their general 

 facies is different from any series in Normandy or Brittany. There 

 is, however, a certain amount of resemblance between them and the 

 Cambro-Ordovician sequence of Belgium (as described below). 



2. Spain and Portugal 



Rocks of Ordovician age are found in many parts of Spain and 

 Portugal, and the facies which they present in the northern and 

 central parts of these countries is similar to that of Brittany. 

 This facies is well exposed in the cliffs of Asturia on the north 

 coast of Spain. The succession there seen has been described by 

 Professor C. Barrois 27 and compared with that of Brittany 



Asturia. Brittany. 



Calcareous shale of el Homo with Endoceras. \ . , , 



Luarca slates with Calymene Tristani. J An er 



White and green grits and dark slates (Cabo Busto). Gres armoricain. 



Variegated grits with Lingulella Heberti. Gres felspathique. 



The strata are much flexured and faulted, so that accurate 

 estimates of the thickness could not be made, but Dr. Barrois con- 

 sidered the two lower sets of arenaceous deposits to have a thick- 

 ness of from 1200 to 1500 feet. The Luarca slates are probably 

 about 300 feet, and the highest beds about 50 feet. The similar 

 succession found at Almaden in Ciudad Real has been described 

 by de Prado (Bull. Soc. Geol., France, ser. 2, vol. xii. p. 91), and 

 tiiat of Portugal by Delgado in Terrenes Palceozoicos do Portugal 

 vLi&boa, 1876). 



3. Belgium 



the exposures of Ordovician rocks in Belgium are 

 very ^mall, they> are interesting because they and another small 



