48 PALEOZOIC TIME. [CHAP. IV. 



around them as they sank beneath the Silurian sea, till 

 after existing for a time in the condition of atolls, they 

 were eventually submerged and buried under the higher 

 Silurian shales and mudstones. 



It is just possible that another island existed to the 

 south-west of England, and included part of Cornwall, for 

 no rocks of true Silurian age have yet been found in that 

 county, and it is believed that the oldest Devonians rest on 

 the Ordovician rocks of Mevagissey and Veryan Bay. 

 Further examination of this district is required, however, 

 before any definite conclusions can be drawn. 



Basal Silurians exist in Brittany, but nothing comparable 

 to our Wenlock and Ludlow series is found there, and 

 French geologists believe that during the latter part of the 

 Silurian period the Armorican and Cotentin region formed 

 an island the limits of which were very nearly those which 

 are now presented by the pre-Devonian rocks of this 

 district. 1 



1 Lapparent, " Trait< de Geologie," second edition, p. 781. 



