M. Dumont on the Geology of Belgium. 14-7 



swers to the middle system, which I established in 1836, in 

 the slate district of Belgium. 



Our excursions did not allow us to observe whether the 

 lower slate system exists in Wales, which, moreover, must be 

 difficult to ascertain, on account of the changes which must 

 have been produced by the porphyroid rocks of Snowdon and 

 Cader Idris. 



To the east of the middle Cambrian district, there is an 

 assemblage of rocks quite analogous to that which forms our 

 upper slate system in Belgium, which may be proved by 

 traversing the mass situated between Mallwyd and Garth- 

 bibio. 



Further eastward successively appear smperposed with re- 

 markable simplicity, the different divisions which Mr. Mur- 

 chison has distinguished in the Silurian system, and which 

 correspond to the three lower divisions of the anthraxiferous 

 system. 



As I should deviate from the purpose of this report by 

 giving in detail the observations which I had an opportunity 

 of making in Wales, I shall limit myself to pointing out the 

 correspondence between the different members of the Silurian 

 and anthraxiferous formations, in the following table : 



Terrai 



HOUILL 



IN "1 

 lER. j' 



r 



Terrain 



ANTHRAX 

 IFERE. 



Terrain 

 ardoisier 



Systeme 



calcareux 



superieur. ^ Calcaire 



r Coal- measure. 



^Millstone grit. 



f Calcaire "j 



^ Dolomie >• Carboniferous Limestone. 



Old Red Sandstone. 



r Psammite Upper Ludlow rock. 1 



\ Calcaire subordonne Aymestry Limestone. I 



\ 



VVenlock 

 formation. 



nuarzo^schisleuv i ^'^''^""''^ ^"'^°'''^°"^^ Aymestry Limestone. I Ludlow 

 superieur. ' ] ff''!'^f •.......•• Lower Ludlow rock, [formation. 



•^ \_Lalcaire subordonne J 



Systeme f Calcaire ...."] 



calcareux < Dolomie I W enlock Limestne. 



iiiferieur. |_ Calcaire J 



Systeme { Schist gris fossilifere...\i exAock 8\\a[c. J Caradoc & 



quarzo-schisteux < Schiste et psammite rouge, poudingtte. \ Llandeilo 



infer ieur. (_ Psammite, quarzite, schiste. j formation. 



Superieur 1 



Moyen I Cambrian 



hijirieur '..".'.1'.'.*.".!'.'.'.!',*.".'.'.".".*.". J SYSTEM. 



On the mere view of this table we are struck with the 

 agreement which there is between the two districts ; and in 

 fact, all the Belgic divisions recur in England in perfect 

 succession. There is however a difference in their general com- 

 position which it maybe useful to mention ; it consists chiefly in 

 the somewhat rudimentary state to which the calcareous rocks 

 are reduced. Thus, whilst in the Eifel and the southern part 

 of the provinces of Hainault, of Namur, and Liege, the lower 

 calcareous deposit acquires an enormous developement, the 



L2 



