238 



THE ROCKS OF ALDERNEY. 



fossiliferous rock hitherto found in north- 

 western France. 

 3rd. — That the fossils of the " Gres armoricain " 

 establish its correspondence with the Arenig 

 rocks of Wales and Shropshire. 

 The Gres armoricain is the quartzite found at Cherbourg, 

 Falaise, Domfront and Mortain, in Normandy, and which runs 

 through Brittany, terminating near Brest. It follows that 

 the Alderney grit is somewhat, but probably not much older 

 than the Arenig rocks ; as there appears to be no unconform- 

 ability between it and the Gres armoricain. M. Bigot con- 

 siders it to be contemporaneous with the " Lingula Flags." 

 It would therefore be Lower Silurian according to the nomen- 

 clature adopted by the Geological Survey, but would be placed 

 either at the base of the Ordovician or summit of the Upper 

 Cambrian, according to the system proposed by Lapworth, 

 which is viewed with increasing favour by geologists. The 

 Alderney grit, as will be seen by the diagram, is a newer 

 formation than the Jersey conglomerate. 



DIAGRAM. 



Typical Rocks of 

 England & Wales. 



Nomenclature.* 



ABC 



French Rocks accord- 

 ing to M. Bigot. 



Channel Island 

 Rocks. 



Ludlow Series 



Wenlock „ 



Mayhill ,, 



Bala „ 



Llandeilo ,, 



Arenig ,, 



Tremadoc , , .... 

 Lingula Flag Ser. 



Menevian ,, 



( Solva . . 

 Harlech < 



( Caerfai. 



Precambrian 



I 





s 



m 



Gres Armoricain. 

 Gres Feldspathique. 



Schistes Vert Clair. 

 Schistes Pourpres. 

 j Gres et Conglo- ) 

 \ merat Pourpres. J 



Schistes de St. Lo. 



/ Alderney 

 \ Grit. 



( Jersey Con- 

 \ glomerate. 

 ( Jersey Ar- 

 \ giliites. 



pi 



3 

 1 



w 



I 



o 



1 



O 



<D C3 



m 



^d 



Pi 



o 



Si 



o d 



o 



1 



1 











* The nomenclature in column A is that adopted by Sedgwick : in column B, 

 that of Murchison, adopted by the Geological Surveys of England and France : in 

 column C, Lapworth's. 



