G. Dewalque on the Cambrian Rocks. 43 



(Bull. 2nd ser. torn, xxxiv. p. 424) that a comparison between them 

 and the analogous formations of our country had enabled me to 

 establish the parallelism of the subdivisions of the Cambrian rocks 

 in both countries. I then hoped to be soon able to draw up a 

 detailed communication on the subject, but my health has until now 

 prevented my doing so. As I have had occasion to lay before my 

 pupils the results of my observations, I think it may be useful now 

 to make known the parallelism which I believe I have determined. 



I have long ago regarded our "Ardennais" formation as Cambrian, 

 notwithstanding contrary assertions. The Cambrian of North Wales 

 is represented, according to most authors, by the Harlech grits, the 

 Llanberis slates, the Lingula flags, and the Tremadoc slates. The 

 two first names are applied to two series which I consider as con- 

 temporaneous : their characters bear the same relations to each other 

 as those of our two " devilliennes " bands of Montherme and Furnay, 

 which they exactly resemble, except that our quartzites are there 

 often replaced by conglomerates. The slates of Furnay and those 

 of Llanberis are absolutely identical. 



Our " systeme revinien " corresponds quite as exactly to the 

 Lingula flags ; the likeness of the rocks is perfect. 



"With regard to our " systeme salmien," it must be noted that its 

 lower limit is not very clear, and that it has usually undergone a 

 peculiar metamorphism, which scarcely allows one to hope to meet 

 with similar rocks in Wales. I think I am justified in placing it on 

 the horizon of the Tremadoc slates, because of the position occupied 

 by both these formations between the "systeme revinien" or Lingula 

 flags and the great dislocation which terminates the Cambrian period. 

 It will be noticed that the Tremadoc system is a local formation, like 

 our " systeme salmien." 



Some geologists may find these resemblances insufficient to esta- 

 blish the parallelism in question. I think I can promise that the 

 primordial fauna will be found in our " systeme revinien." I have 

 just recognized, in a specimen which had long been looked upon as 

 indeterminable, a plant which is characteristic of the Fucoidal grits 

 of Scandinavia, Eojjhyton Linneanum, Tor. ; it comes from the 

 "revinien" of Stavelot. This genus is also found in the Lingula 

 flags of England. Some years ago I had discovered a Dictyonema at 

 Spa, at the base of the " Salmien." I have several times taken my 

 pupils to this spot, and last year several specimens were found. 

 Since then I have assured myself that it is the Dictyonema sociale, 

 Salt., of the Upper portion of the Lingula flags (which would tend to 

 alter the inferior limit of the " Salmien "). 



I may add that I have met with the same species in the same 

 position at Buy, during the excursion which I made last spring with 

 my pupils. 



