278 Professor Sedgwick and Mr. Murchison on the 



in the upper part of the series, occupying the central portions of the several troughs ; while on the 

 outskirts of the formation we often see masses of unaltered and well-bedded limestone rising from beneath 

 the great ridges of dolomite, and so forming the base of the troughs. 



It is hardly possible to resist the impression that a great part of this formation has an altered 

 structure ; and when we remarked the numerous lofty cones of cellular and basaltic lava which studded 

 many parts of the region — the great inverted cones breaking through the limestone, and containing cin- 

 ders, scoria, and other indications of ancient volcanic vents — the great fissures in the Dolomites of Gerol- 

 stein, through which streams of lava and masses of scoria have mounted to the surface — above all, when 

 we considered the wide-spread volcanic products which for several leagues cover up the whole eastern 

 limits of the formation, we at first thought that we had before us the obvious causes of all that complexity 

 of mineral structure which we have noticed. 



Fig. 13. 



Gerolstein. 





Bands of Upcast. 

 limestone in shale. 



Subsequent observations induced us to modify this opinion ; for Dolomites occur at great distances 

 from any of the modern volcanic vents. Moreover, these vents have produced a very small effect on the 

 strike or inclination of the beds in any of the older formations*. Hence it is probable, that the chief mine- 

 reJization of the Eifel limestone took place during some of those early periods of plutonic disturbance, 

 during which the older strata of the Rhenish provinces were elevated and contorted. Before we quit 

 this subject, we may remark, that the causes which mineralized the rocks of the Eifel may, perhaps, have 

 driven off" the carbonaceous matter they once contained ; for we find among them none of those black 

 beds which are so frequent in the lower limestones of Belgium and Westphalia. 



Many of the fossils of the Eifel limestone are well known, among which are found certain Silurian 

 species. These are however chiefly derived from the inferior shales, which we have not yet noticed ; and 

 it is important that the fossils of the upper and lower portions should be kept distinct. M. Beyrich 

 of Berlin, whom we have before quoted, saw the importance of this distinction ; and has, without any 

 assumed hypothesis, and merely from the characters of the fossils, separated the limestones of Bensberg 

 into two distinct formations. It is enough for us to observe in this place (referring for further evidence 

 to our lists), — that the group of fossils in the Eifel limestone is Devonian — that we there find great 

 masses containing Strigocephalus Burtini, and other well-known Westphalian species (which we never met 

 with in the strata below the great Westphalian limestone) — and that nearly all the Silurian types which 

 characterize the lower group are entirely wanting. We therefore place the great Eifel limestone on the 

 parallel of the lower Westphalian and Belgian limestones, and consequently the lower part of the Devo- 

 nian system. In this arrangement the conclusions derived from the sections and the groups of fossils 

 are in harmony with one another. 



* As examples of what is stated in the text, we may instance the beautiful volcanic lakes near Daun and 

 Gillenfeld, and the great crater of Bertrich. At these points of eruption the slate rocks of the country 

 are very little mineralized, and have undergone no sensible change in their strike and dip. 



