270 Professor Sedgwick and Mr. Murchison on the 



successive groups (as far as they are exhibited) are in the ascending order of the 

 series above given. 



For example, if from this centre we ascend the gorges of the Meuse towards Mezi- 

 ^res, we pass in succession over the 4th and 3rd groups, when the series is inter- 

 rupted by the unconformable junction of secondary strata. If, on the contrary, we 

 take any line of traverse down the basin of the Meuse, toward the Belgian coal-field, 

 we cross in regular ascending order the several groups of deposits (before enumera- 

 ted) , ending with the carboniferous system. Now these groups or systems are ar- 

 ranged symmetrically, are conformable to, and pass into, one another. They can 

 therefore only belong to a consecutive series of deposits ; and as we are certain of 

 the relative ages of the carboniferous system, and that which is next in order, we at 

 once conclude that we have from that system, to the very centre of the Ardennes, a 

 true descending section. And thus we bring the geological sequence into harmony with 

 the mineralogical phaenomena ; which never could have been done, for reasons already 

 stated, by examining the superposition of the beds on any one line of traverse. 



The central crystalline schists, above mentioned {roches aimantiferes, &c., of 

 M. Dumont), do not form any distinct continuous ridge, but break out here and 

 there, nearly along the prevailing line of strike, and with the relations above in- 

 dicated. Their last appearance towards the N. E. is in a wild mountainous tract 

 near Recht, a village eight or ten miles south of Malmedy ; and taking these slates 

 as a centre, if we make traverses from them to any part of the Liege coal-field, we 

 cross the 4th, 3rd, and 2nd groups, above enumerated, and so pass into the 1st or 

 carboniferous system. The groups are conformable, continuous, and pass insensibly 

 one into another. They must therefore belong to an uninterrupted geological se- 

 ries ; and we determine the superposition, as before, not by the evidence of vertical 

 sections, but even in some cases in direct opposition to it ; for the magnificent 

 sections seen in the various gorges, as we approach the coal-field of Li^ge, generally 

 exhibit an inverted series*. 



In making another traverse from the same geological centre, near Recht, to the 

 limestone of the Eifel, we cross, in regular ascending order, the two zones of roof- 

 ing slate (groups 4 and 3) ; and then, after passing over the lowest division {systeme 

 quartzo-schisteux inferieur), finally arrive at the lower limestone of Dumont's 

 second system (terrain anthraxifere). Thus we have another proof of the truth of 

 the greater part of our geological sequence ; and, as far as the section is complete, 

 we obtain also a new proof of the true order of superposition : for on the Eifel side 

 the beds are no longer inverted ; and the evidence derived from considerations of 

 symmetry in the horizontal distribution of the mineral masses is in perfect accord- 

 ance with that which is given by the clear vertical sections f. 



* See Plate XXIII. fig. 12. f See PI. XXIII. fig. 12. and fig. 14- 



