60 STRATIGRAPHICAL GEOLOGY 



granite, occupy large parts of Brittany, together with the western 

 portions of Normandy, Maine, and Anjou. They have been well 

 described by Professor C. Earrois, from whose memoirs the following 

 account has been compiled. 29 He and other French geologists are 

 inclined to divide them into two main series which they call (1) 

 Archaean and (2) Brioverian, but as they again subdivide the lower 

 series into three portions, and as no break has been observed 

 between any of the divisions, they can be equally well arranged in 

 three series, thus : 



3. Phyllades des St. Lo ( Brioverian). 



2. The nrica-schists of Groix. 



1. The schists of Audierne and gneiss of Quimperle. 



The oldest group is a complex of which a granitoid rock some- 

 times seems to be the oldest member, but more often the lowest 

 rocks are mica-schists which include bands of ribboned gneiss, white 

 leptynite, amphibolite, and eclogite. In the south these rocks form 

 a continuous tract from 10 to 16 miles in breadth extending from 

 the Bay of Audierne on the west to the valley of the Loire, a 

 distance of about 140 miles. In the north there are two bands 

 of similar rocks, one passing from Brest to Leon with probably a 

 submarine continuation to Guernsey, the other near St. Malo. 



Professor Bonney informs me that he has not seen anything in 

 Western or Northern Brittany, nor in the Cotentin, which is quite 

 comparable with the Hebridean and Malvernian gneiss, and he is 

 inclined to doubt whether such gneiss exists in the region. 



The schists of Groix seem to be an upward continuation of 

 the series, being truly crystalline schists of micaceous, chloritic, 

 graphitic, and sillimanitic varieties, with subordinate bands of 

 quartzite (sericitic and graphitic), hornstone, and pyroxenic marble 

 (cipolin). These resemble the Loch Maree Beds. 



The Brioverian Series consists of much less altered rocks of a 

 typical Eparchsean character. They exhibit three different facies 

 in different parts of the region : (a) the facies of St. Lo in Normandy 

 and of Central Brittany, comprising the phyllades of St. Lo and 

 Lamballe, the phyllades of Gourin, which include a band of 

 limestone, and the green flags of Neant at the top ; (6) the 

 Tre"gorrois facies in the north of Brittany, consisting of phyllades 

 and quartzose rocks with interstratified eruptives (porphyrites and 

 diabases) ; (c) lastly, the southern facies, which consists mainly of 

 shales with interbedded bands of coarse felspathic sandstone, 

 recalling the Torridonian of Scotland and suggesting that the 

 Brioverian land lay to the south of Brittany. 



These Brioverian deposits are unconformably overlain by the 





