older Deposits of the North of Germany and Belgium. 275 



formation we are considering. Again, at Martelange, on the south flank of the Ardennes, and in this 

 upper zone ot' slates, we find several species of fossils ; e. g. 



(1.) Beautiful starred Encrinites, like those (figured in our Devonian paper) which were found near 

 Looe in Cornwall, in a rock considerably inferior to the Plymouth limestone*. 



(2.) Two species of Orthoceras, and one we think identical with Orthoceras arliculatum of the Ludlow 

 rock. 



(3.) A trilobite not easily distinguished from Homahnotus Knightii of the Ludlow rock. (Fig. 11.) 



Fig. 11. 



These fossils (and some others which we saw in the museum of Namur through the kindness of Pro- 

 fessor Cauchy) first led us to think that the slaty zone we are considering was partly Devonian and partly 

 upper Silurian ; we afterwards, however, modified our opinion, finding that certain forms found in only 

 the highest part of the Silurian system in England, are more widely diffused, and descend into the lower 

 part of it on the Continent. On the whole, we conclude, partly on direct evidence and partly on ana- 

 logy, that the upper slate zone (sgsteme ardoisier superieur) of Belgium and the Ardennes (and with it we 

 would also class the lower part of the formation immediately overlying it) is of the Silurian age, though 

 its mode of development offers us no means of separating it into distinct groups ; and thus the whole fos- 

 siliferous system, from the mountain limestone downwards, forms one connected and natural series. 



6. It is in vain for us to enter on any details respecting the oldest slate rocks of the Ardennes, and of 

 the country between Liege and the Eifel, as we have not obtained a single fossil from them. As, how- 

 ever, they form only the last term of a connected series and immediately succeed the Silurian system, 

 we see no reason for placing them lower than the upper Cambrian system. Their mineral character op- 

 poses no difficulty to this view, as we know by the analogies presented by the slate rocks of our own 

 country, how impossible it is to determine their age by mere considerations of mineral structure. 



Before we quit the consideration of the Belgian rocks, we may, however, notice the 

 beautiful structure of the old slates of Recht, which form the axis of the country south 

 of Malmedy f. The slates are obtained by planes of cleavage distinct from the beds, 

 and sometimes dipping to an exactly opposite point ; and the true bedding is marked 



* See Geol. Trans., vol. v. PI. LV. fig. 8. t See Section 12, PI. XXIIL 



