T1IK AKCHJEAN ROCKS 0'J 



district in Devon and the Lizard promontory in Cornwall, and in 

 neither case can the Archiuan age of the rocks be proved became 

 the adjacent strata belong to the Devonian System. 



The area in Devon is that part of the county which lies inside 

 the headlands of Start Point, Prawle Point, and Bolt Head. It 

 has a length of about 9 miles with an extreme width of 3 

 from north to south. The rocks of which it consist* are divisible 

 into two groups, a lower set of mica and quartz schist* and an 

 upper one of green hornblende-epidote schists, known as the Green 

 schists, and obviously altered basic igneous rocks. 



The general structure of the eastern half of the area is that of 

 an irregular anticline, bent over and inverted on the southern 

 side. The northern border is believed to be a fault, and there ia 

 everywhere a rapid if not immediate change from foliated rocks 

 to Devonian slates which are comparatively unaltered, except by 

 cleavage and dislocations. Some geologists have maintained that 

 the schists are only highly altered Devonian slates, and have 

 appealed to the facts, that there is a progressive increase in the 

 intensity of the cleavage in these slates south of Brixham ; that 

 there are appearances of a passage from slates to schists in some 

 places along the boundary line ; and that the general strike of both 

 series is the same, i.e. from west to east. It must be remembered, 

 however, that the dominant flexuring of this part of England dates 

 from late Carboniferous time (Armorican folding), while the 

 appearance of a passage may be caused by the occurrence of 

 crushed and broken schists between two lines of fault If this 

 area is altered Devonian the metamorphism can only be due to the 

 influence of some local cause, such as the existence of a subterranean 

 mass of granite, but the balance of evidence seems to be in favour 

 of their Archaean age. 28 



C. AKCH^EAN ROCKS IN EDROPI 



Outcrops of Archsean rocks, or what are generally regarded w 

 Archaean rocks, occur in France, Spain, Switzerland, Austria, 

 Bohemia, Saxony, the north of Russia, Finland, and Scandinavia, 

 Only the more important of these areas can here be described. 



1. France 



In France the chief exposures are found in the north-wot 

 (Brittany and Normandy) and in the Central Plateau. 



Brittany. Pre- Cambrian rocks, with associated nuase* of 



