older Deposits of the North of Germany and Belgium. 279 



Shales, Red Psammites, Schists, 8fc., under the Eifel limestone, 

 {h^ of coloured Sections, Figs. 10, 12, 13, and 14, PI. XXIII.) 



The formation beneath the Eifel limestone is essentially the same, on whatever 

 side we begin our examination. 



We have first a series of shales more or less calcareous, alternating with the bands of limestone, and 

 passing into the state of indurated marl. In its upper portion this group passes into, and blends with, 

 the great overlying limestone. In its lower portion it begins to alternate with psammite and flag- 

 stone ; the alternating shales lose their marly character, become more meagre and arenaceous, and are 

 occasionally of a reddish tinge. The same colours are not unusual in the flagstones. Here and there 

 the marly beds, along with courses of limestone, reappear at considerable depths in the descending sec- 

 tion ; but at length the formation passes into a vast deposit of flagstone and psammite, with bands of meagre 

 shale and earthy schist repeated in many alternations. 



The development of the series (though differing considerably from that of the 

 corresponding deposits of Belgium) is almost exactly similar to that on the right 

 bank of the Rhine under the lower Westphalian limestone ; for there we have the 

 same recurrence of thin calcareous bands, the same alternations and mineralogical 

 characters, again and again repeated; so that one description might almost do 

 for both. Near Daun, Pr'dm, Cronenburg, Miinster-Eifel, and Euskirchen, there are 

 clear sections, which prove that the strata underlie the great mass of lime- 

 stone : and at these localities we found at least four species of Orthis, one of 

 which approaches very closely to Orthis orbicularis, and another to Orthis or 

 Leptana lata, of the upper Silurian rocks. With these fossils are grouped certain 

 Trilobites, which we cannot distinguish from published Silurian types, such as 

 the Calymene Blumenbachii, C. macrophthalma, and two or three forms of Homa- 

 lonotus, one of which resembles closely the H. Knightii. They are occasionally 

 associated with the Delthyris macroptera and D. microptera, and with numerous 

 Tentaculites. Thus the group we are describing is shown to be identical with that 

 of the Lahn mouth, of Braubach, and of other places on the right bank of the 

 Rhine, which we have considered as upper Silurian. 



Notwithstanding therefore some difference of development, we are led (as we 

 were on the other bank of the Rhine) to place this portion of our section in 

 the upper part of the Silurian system. In this view, the upper marly shales 

 can be regarded only as beds of passage, zoologically as well as mineralogically, 

 between the Eifel limestone and the Silurian system. Now as many of the 

 published Eifel fossils are derived from these marls, which contain an immense 

 number of well-preserved organic remains, we need not wonder, on this explana- 

 tion, at the occurrence of so many well-knoivn Silurian types among these published 

 Eifel lists. 

 The analogy between this and the corresponding group on the right bank of the 



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