490 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 20, 



4. Verneuilii-Schiefer, Ar- 1 Marwood (and Pilton ?) Group, with 

 gillaceous Sandstone. J exactly the same fossils. 



These Verneuilii-Schiefer (a bad name for a group already named 

 by Sedgwick and Murchison) come up in long parallel folds near 

 Aix-la-Chapelle and rest on the Eifel-Kalk, without the intervention 

 (at this place) of the Cypridina- Schist, and are themselves covered 

 by the Kohlenkalk or Mountain Limestone. This fact is valuable, 

 as indicating what we have as yet failed to detect in North Devon — 

 an unconformity between the Marwood group and the other mem- 

 bers of the Devonian formation*. 



In the Bas Boulonnais, Sir Roderick Murchison described, in 

 1840, some of the Devonian species, but failed to make out that the 

 whole series was only the uppermost portion of that formation ; nor 

 was Mr. Godwin-Austen, in 1853 f, completely set free from the 

 notion of older Devonian rocks being present, as Delanoue and others 

 had determined. 



But Mr. Austen's paper gives all the necessary elements for 

 correcting this view ; the stratigraphy is clear, and the lists of fossils 

 complete. Below the Mountain Limestone he found a band of shale 

 (Le Hure, Ferques, &c), which he passes over without much com- 

 ment, but which must either be the Limestone-shale or the Pilton 

 group, and his paper conducts us at once to 



The Yellow Sandstone group = " Gres a Unio " of Eozet [Psammite 

 de Ludlow, of the Boulogne Meeting J], Landrethun to Ferques, 

 25 feet thick (Bois de Beaulieu, &c), meeting the Coal-mea- 

 sures (Dufrenoy), Marwood Sandstone (Austen). 



There can be no doubt of the age of this sandstone. Cucullcea 

 Hardingii, C. trapezium, Bellerophon subglobatus, &c, tell the story 

 at once, and leave us free to consider the strata below them. 



If the Boulogne formation were anything like the same in deve- 

 lopment as our North Devon series, the thickness of 25 feet of sand- 

 stone would give us a mere capping for the great Marwood series ; 

 accordingly we find, in descending order, 



Bright red shales and clays. ] ™ ., i -r?- 



-r. i , -, J > Chateau de liennes. 



Dark grey shales J 



Ferques limestone. — Near Malaise, Bois de Beaulieu, and to the 

 Chateau de Fiennes. Great abundance of Spirifer disjunctus. 

 A selected list of the fossils of this limestone gives us the true Pil- 

 ton group. We have Athyris cohcentriea, ffliynchonella pleurodon, 

 Spirifer Bouchardi, S. disjunctus, Strophcdosia caperata (S. scahricu- 

 lus, Sharpe), and Phacops latifrons (P. Latreillii). With these, how- 

 ever, are a few which are more characteristic of the Newton-Bushel 

 limestones than the Barnstaple group, namely, Atrypa retiadaris, 



* Unconformity to the largest extent has long been known between the Upper 

 and Lower Old Red in South-west Ireland. Sir R. Griffith described it ; Sir R. I. 

 Murchison, Mr. Jukes, the Members of the Geological Survey of Ireland, and 

 myself saw it in 1856 ; and since then Mr. Geikie has described the same thing 

 as occurring in Scotland. See Quart. Journ. Geol. Soc. vol. xvi. p. 312. 



t Quart. Journ. Geol. Soc. vol. ix. p. 231, &c. 



£ Bulletin de la Societe Geologique de France, vol. x. p. 404, 1840. 



