578 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



the presence above the Benan conglomerate of the extensive series of 

 Caradocian sediments with marine fossils, whereas in America emergence 

 continued during the equivalent Upper Trentonian time. 14 The Benan 

 conglomerate overlaps the earlier Llandeilo beds southward, where it 

 comes to rest directly on the disturbed and eroded surfaces of the Arenig 

 volcanics. 



Lake District. — It is possible that the whole of the Arenig is repre- 

 sented in the great series of Skiddaw shales in the Lake District, and 

 some Llandeilo may even be included in the upper part of the series. 

 Most of Llandeilo time, however, was occupied by the eruption of the 

 great Borrowdale volcanic series, which continued into Caradocian time, 

 for late Caradocian strata alone succeed this series. This region was thus 

 probably land during the whole of Middle Ordovicic time, as there is no 

 reason to assume that the eruptions were of a submarine character. 



Wales. — In the Welsh region, on the other hand, deposition seems to 

 have been continuous from Arenig into Llandeilo time, as indicated by 

 the transitional facies for which Hicks has coined the term Llanvirn 

 series. This comprises some 2,000 feet of shale near Saint Davids. 15 



Normandy and Brittany. — Turning now again to the southern border 

 of the English Lower Ordovicic sea, we find the Arenig represented in 

 Normandy and Brittany by the Armorican grit (Ores Armoricain), a for- 

 mation consisting mostly of white quartzite and ranging in thickness up to 

 500 meters in Brittany, 10 and well exposed along the coast of the Crozon 

 Peninsula between the Bade de Brest and the Baie de Douarnenez. The 

 beds of this region are thrown into a series of isoclinal folds which have 

 a steep dip to the north, the southern limbs of the folds being overturned 

 and the whole complicated by faults and by diabase dikes and -other 

 intrusives. 



The general strike is east-west, though pronounced local variations 

 occur. In this section the Armorican grit rests with a disconformity on 

 the Upper Cambric Lingula sandstones (schistes pourpres), which in turn 

 rest on the Paradoxides beds, and these are disconformably preceded by 

 the Brioverien series of phyllites, sandstones, conglomerates, and cal- 

 careous beds (also called the Phy Hades de Saint L6), the oldest sedi- 

 mentaries of Brittany and regarded as of pre-Cambric age. The Ordo- 

 vicic series begins with the Erquy pudding-stone, a coarse conglomerate 

 composed of fragments of the sediments and eruptives of the Cambric. 

 This is followed by a coarse-grained, feldspathic, non-fossiliferous grit, 



14 A. W. Grabau : Early Paleozoic delta deposits. Bull. Geol. Soc. Am., yoL 24, pp. 

 399-528. 



15 Hicks : Pop. Science Review, 1881, p. 289. 



16 Ch. Barrois : Guide de Bretagne, p. 10. 



