Ixvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



merits of M. Dumont's Essay, but simply to show how impossible it 

 is to determine the relative ages of the strata of the earth without an 

 appeal to the fossils, or, in other words, to the Natural History, of 

 each successive epoch. M. Dumont detailed with the utmost ability 

 the mineral structure and the physical peculiarities of the province 

 of Liege, and his work became a natural basis for the future researches 

 of himself and others ; but a district so much undulated by disturb- 

 ance was not to be satisfactorily unraveled by such a system of in- 

 vestigation alone. The identification, however, of the Lower Quartz- 

 schist of the Anthracitiferous formation with the Old Red Sand- 

 stone, and the determination of two successive limestones, the lower 

 and the upper, were important steps towards the final establishment 

 of the Devonian as a true formation. 



In his subsequent memoirs on the rocks of the Ardennes and of 

 the Rhine, M. Dumont observes that in his preceding work he had 

 proved the accuracy of M. D'Omalius d'Halloy in dividing the pri- 

 mary strata of the North of France into the Slate, Anthracitiferous, 

 and Coal formations ; and he then adds that subsequently Sir R. 

 Murchison had proposed for the same formations the names of Silurian, 

 Devonian, and Carboniferous, — denominations which, having been 

 adopted by many French geologists, had replaced those of D'Halloy* 

 M. Dumont also admits that the undulations and disturbances of the 

 four systems into which he had divided the Anthracitiferous forma- 

 tion produce such indefinite alternations of the calcareous, schistose, 

 and quartzose divisions, as to render their study very difficult, 

 though he states that by purely geometrical considerations he suc- 

 ceeded in demonstrating the existence of two calcareous deposits 

 within the Anthracitiferous formation, and adds that Murchison 

 had arrived at the same result in England, having allocated the 

 Lower limestone to the Devonian, and the Upper to the Carboniferous 

 formation. Without doubt the labours of M. Dumont were in this 

 respect most valuable, as affording a proof of the just claim of the 

 Old Red Sandstone to be considered part of a true formation, and 

 his observations correct ; but his subsequent remarks are not equally 

 well-founded, when he speaks of the difficulties which those first-rate 

 geologists, Sedgwick and Murchison, experienced in determining the 

 precise boundary between the Cambrian and Silurian formations, as 

 proofs of the insufficiency of a study of organic remains to settle such 

 questions. This idea he endeavours to strengthen by pointing out 

 the differences of opinion which have existed in respect to the quartz- 

 schist of the Ardennes and of the Rhine, which Sedgwick and Mur- 

 chison had placed in the Silurian, whilst M. C. F. Roemer had con- 

 sidered, from the study of organic remains, that the quartz-schist 

 of the Rhine belonged to the Devonian, and MM. D'Archiac and 

 De Yerneuil, from their examination of the ancient fossils of the 

 Rhenish Provinces, had placed the grey slates of Meder-Priim in the 

 Silurian, though, in M. Dumont's opinion, above the red grits of the 

 quartz -schist- system of the Anthracitiferous formation; and he then 

 concludes that Palaeontology had proved insufficient, and proceeds to 

 establish the divisions of the ancient Schist-formations by his own 

 geometrical method. 



