276 Professor Sedgwick and Mr. Murchison on the 



on the slates by the usual appearance of a stripe, or sedimentary line. In addition 

 to the main cleavage there is in some of the quarries a distinct second cleavage, 

 indicated by an infinite number of minute stricB, which maybe traced even through 

 the minutest portions of the slates. This shows that the stries and second cleavage 

 were derived from a true molecular action, quite different from the mechanical ten- 

 sion which has so often produced large open joints. The second cleavage is not 

 sufficiently perfect to produce any roofing slates, and indeed in some measure in- 

 jures those obtained from the first and ordinary cleavage ; for all the slates have a 

 tendency to break off" at the regular planes presented by the second cleavage. 

 Large masses of the rock had, in some places, slid off" in the quarries at one of the 

 second cleavage planes ; which, being highly inclined to the horizon and nearly 

 transverse to the bedding, gave the appearance of regular dip-joints. But they 

 are xioi joints in the common acceptation of the term, and they are cut at a small 

 angle by nearly vertical true dip-joints ; which, as usual, intersect both the beds 

 and cleavage planes without deviating from their course. We have never remarked 

 phgenomena such as these in Cumberland, Lancashire, or North Wales ; but in a 

 previous paper we noticed similar (though in their kind less perfect) appearances 

 on the coasts of Devonshire and Cornwall*. 



Eifel, Banks of the Rhine, Basin of the Moselle, &;c. 



We have before stated, that if we commence with the oldest slate rocks near 

 Recht, and make two ascending sections, one to the lower limestone of Belgium, 

 and the other to the limestone of the Eifel, we pass through the same succession 

 of deposits! . Hence we might conclude, on the general evidence derived from 

 this physical structure (and the conclusion is also borne out by the fossils), that the 

 two limestones are on the same parallel. On this point, indeed, there seems to be 

 no difference of opinion. Now in the whole region, extending through the basin 

 of the Moselle to the Hundsriick, and on the left bank of the Rhine from Bonn to 

 Bingen, there are no repetitions of any great limestone groups ; such as are seen 

 in the Eifel, and on the other bank of the Rhine along the drainage of the Lahn, 

 and in the mineral country of Dillenburg. In short, all the deposits of the regions 

 above alluded to, on the left bank of the Rhine, are inferior to the Eifel lime- 

 stone, which may therefore be assumed as a fixed point of departure in the de- 

 scending sections. 



One of the chief masses of this limestone (see Map, PL XXIV.) occupies an irre- 

 gular elliptical area, the longer axis of which extends from a point a little S. of 

 Schonecken to a point about two or three miles N.E. of Miinster-Eifel, and is sur- 

 rounded by the formations which are immediately inferior to it. Its true position 

 * See Geol. Trans., vol. v. pp. 656 and 658. f See PI. XXIII. fig. 12 and fig. 14. 



