older Deposits of the North of Germany and Belgium. 273 



colour. The schists pass into arenaceous shales alternating with flagstones ; and at their lower boundary- 

 pass into slaty masses which blend themselves with, and are inseparable from, the upper slate rocks of 

 the next lower system (systeme ardoisier superieur of M. Dumont). 



Considered as a whole, this formation is harder and more siliceous than the upper quartzose schists 

 above described. It is also distinguished (though to this remark there are many exceptions) by the red 

 colour, not merely of the conglomerates above noticed, but also of the flagstones and shales, which some- 

 times are both red and variegated*. These colours are most prevalent within a certain distance of the 

 limestone, and disappear in the descending sections. The flagstones and associated arenaceous shales 

 are, however, often of a grey, yellowish-grey, and greenish-grey colour, and sometimes pass into the condi- 

 tion of an earthy mudstone, like the upper Silurian rocks of England. Occasionally (though not com- 

 monly) traces of an oblique cleavage may be seen among the more slaty masses, and the whole is often 

 divided by a double system of joints. And we may remark, that such joints cut through the conglome- 

 rate beds by regular plane surfaces which continue their course through the imbedded pebbles without 

 any interruption ; thereby showing that the force which produced the joints was of the nature of a me- 

 chanical tension (by what cause produced we do not now inquire), and not derived from any direct 

 molecular action of the particles composing the jointed masses. 



The formation is of great thickness in Belgium ; but, as far as we are able to interpret the sections, it 

 is .vastly thicker, and also more calcareous and fossiliferous, in the country south of Westphalia, and also 

 in the country surrounding and dipping under the Eifel limestone. 



For the fossils of this formation (which are difficult to procure, and of which we brought away hardly a 

 single specimen) we must refer to the lists of M. Dumont ; and also to our lists, derived from rocks of the 

 same age, beyond the limits of the country we are now considering. As we can show that the formation im- 

 mediately below it is unquestionably Silurian, we are justified in placing it between the undoubted Devonian 

 and Silurian rocks. But where shall we draw the line of separation ? We shall endeavour to find an answer 

 to this question in evidence afforded by the sections of the Eifel and the Rhenish provinces, which are 

 more complete. Meanwhile we may observe, that the mineral character of the red conglomerates which 

 appear below the inferior limestone, formerly led M. Dumont (to whom we may add M. Rozet and other 

 observers) to regard them as the representatives of our old red sandstone. We have not any great ob- 

 jections to this view ; and adopting it hypothetically, we should place the conglomerates and the coarse 

 hard beds which occur in the upper part of the formation we are now discussing at the base of the De- 

 vonian system (or old red sandstone). On this view, it follows that the inferior Belgian limestone and 

 all the overlying deposits up to the base of the superior (or true mountain) limestone must represent the 

 middle and upper portions of the old red sandstone. Nor do we think it any objection to this deter- 

 mination, that the assumed base line cuts through a natural mineralogical group, so as to place its upper 

 and lower portions in two distinct systems ; for the same objection may be made to the zoological sub- 

 divisions of the deposits in the Paris basin, as well as to some of the lines separating the secondary 

 formations of England. 



We endeavour to show that the transition formations of the Continent, com- 

 mencing with the mountain limestone and descending to the lowest fossiliferous 

 deposits, form one vast uninterrupted sequence, with no universal and well-defined 

 subdivisions : and we also attempt to show that the natural groups of fossils follow 

 a similar law. The mineralogical groups and the fossil groups being both founded 

 in nature, and presenting an actual sequence, agree in the general and broad con- 



* See Plate XXIII. fig. 12. 



