﻿DEBEY ON THE AIX-LA-CHAPELLE DISTRICT. 



109 



10. Pecopteris (Aplophlebis) arborescens, Brong. 



11. P. (A.) allied to P. unita, Brong. 



12. P. (A.) resembling P. cequalis and aspersa. 



13. P. (A.) allied to P. arborescens, Brong. 



14. P. (Dicrophlebis) cyathea, Brong. 



15. P. (D.) Bucklandi, Brong. 



16. P. (D.) allied to P. nervosa, Brong. 



17. Calamites, sp. 



18. Annularia longifolia, Stemb. 



[T. R. J ] 



Sketch of a Geognostico-geogenetical Description of the Aix-la- 

 Chapelle District. By Dr. M. II. Debey. pp. 67. 4to. 

 Aix-la-Chapelle. 1849. With a Lithographic Plate of Sections. 



TEntwurf zu einer geognostisch-geogenetischen Darstellung der Gegend von 

 Aachen, n. s. w.] 



This memoir is a short sketch of a more extended monograph on 

 the rocks and fossils in the neighbourhood of Aix-la-Chapelle, and 

 more especially on the Cretaceous series of that district. This For- 

 mation is here remarkable for its lower sand- and clay-beds, which 

 contain a rich and beautiful Flora. 



In dividing the Chalk -formation of Aix-la-Chapelle into groups, and 

 comparing them with those of the classical localities of this Forma- 

 tion in Bohemia, Saxony, and England, the author finds himself at 

 variance with many geologists ; especially as regards the question 

 whether all the Cretaceous deposits of Aix-la-Chapelle are superior 

 to the Gault, or whether beds chronologically equivalent to the 

 Gault, and even to still lower deposits, viz. the Shanklin Sand, are 

 present there. Dr. Debey considers that the latter is the case. 



The geographical distribution of beings is necessarily regarded by 

 the author as of great importance in proving that deposits perfectly 

 synchronous may in different countries present very different faunas 

 and floras ; and he points out that in this manner the Cretaceous 

 basins and gulfs of England, France, Aix-la-Chapelle, Saxony, Bo- 

 hemia, Silesia, &c, may present local peculiarities and little specific 

 identity of organic forms, and nevertheless may contain beds which, 

 by their stratification, geognostic characters, and generic resemblance 

 of their fossils, are unquestionably of identically the same age. 



Commencing with an account of the older rocks of the district, 

 Dr. Debey proceeds to give detailed descriptions of the Cretaceous 

 deposits and of their organic remains. The Aix-la-Chapelle Chalk- 

 formation, having a thickness of 5-600', is described as lying imme- 

 diately on the Greywacke and Carboniferous rocks (as also in Westpha- 

 lia, Bohemia, and Sweden), and constituting a series of littoral deposits 

 of that great Cretaceous sea that extended westwardly between France 

 and Great Britain on both sides of the existing Channel, and east- 

 wardly over North and Central Germany, Sweden, Poland, and 

 Russia, far into Asia. The following serial arrangement (in ascend- 



