574 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



land-mass — Caledonia — limited the English Sea, or more properly Chan- 

 nel, on the north. On the south, in Normandy and Brittany, these beds 

 are likewise wanting, for here the Gres Armoricain, the chief representa- 

 tive of the Arenig, either rests directly on the crystallines or is preceded 

 by red shales of continental origin, which range up to 2,500 meters in 

 thickness, and generally follow on a basal grit and conglomerate, the 

 thickness of which may reach 500 meters or more. A part of this series 

 probably represents continental Cambric, but some of the red shales, 

 marked by Scolithus, Tigillites linearis, and Vexillum desglandei, may 

 represent Lower Arenig or Tremadoc. 



This southern region of continental deposition constituted the old land- 

 mass of Armorica and separated the Ordovicic English Channel from the 

 Mediterranean Basin. For on its southern border, near Cannes and Saint 

 Chinian, in Montagne Noire, we find the Cambric succeeded by beds of 

 Tremadoc age, carrying, however, a series of fossils distinct from those 

 found in the northern area and described and named by Munier-Chalmas 

 and J. Bergeron. These are: Euloma filacovi, Agnostus ferralsensis. 

 Megalaspis filacovi, Asaphelina barroisi, Diciyoceplialites villebruni, D'\- 

 cellocephalus ? villebruni, and Bellerophon oehlerti. These beds are fol- 

 lowed by blue shales with Asaphelina miqueli J. Berg., Niobe ligiiieresi 

 J. Berg., and these by black shales with Amphion escoti J. Berg, and 

 other fossils. These are succeeded by the Tetragraptus shales. In Spain, 

 near Barcelona, the Tremadoc is likewise represented by shales carrying 

 Ogygia. cf. desiderata Barr., Asapliellus cf. solvensis Hicks, Asaph, inno- 

 tatus Barr., Asaph, cf. wirthi Barr., Niobe cf. homfrayi Salter, etcetera. 

 Elsewhere, however, this horizon seems to be overlapped by the Arenig 

 (Gres Armoricain). 11 



ARENIG 



General discussion. — Above the Tremadoc follow the Arenig shales and 

 grits with apparent conformity and with a maximum thickness of 2,000 

 feet. This series, besides containing a number of brachiopocls (Lingula, 

 Orthis, etcetera) and trilobites (^Eglina, Barrandia, Calymene, Illasnns, 

 Trinucleus, Placoparia, etcetera), is especially characterized by grapto- 

 lites. The series is separable into a lower or Tetragraptus zone, contain- 

 ing T. serra (=bryonoides) , T. quadribrachiatus, Didymograptus ex- 

 tensus, D. pennatulus, and the genera Betiograptus, Loganograptns, 

 Clonograptus, Schizograptus, and Dichograptus, mostly types character- 

 istic of our Lower Deepkill shales of the Hudson Valley. The Upper 

 Arenig is characterized by Didymograptus bifldus. D. patulus, Climaco- 



11 A. Douvlll£ : Handb. Reg. Geol., Bd. iii, 3, Heft 7. 



