GEOLOGY OF THE VEZERE. 33 



and dislocations, as is usual with such rocky strata. One of these " faults " in 

 particular is conspicuous in the precipitous hill-side bordering the valley of 

 the Vezere, between Le Moustier and La Madelaine. 



We must refer the reader to the books and memoirs of MM. d'Archiac, Hubert, 

 Coquand, Arnaud, Harle, and other eminent geologists of France, for detailed 

 descriptions of these Cretaceous Limestones, which, deeply channelled by the 

 Vezere for nearly thirty miles, and cut into by its many tributary valleys, are on 

 nearly all their precipitous escarpments excavated by natural agencies and the 

 hand of Man into galleries, recesses, and caverns, which here and there have been 

 elaborated into residences with stairs and chambers. A general idea, however, 

 of their characters and structure, useful to the passing observer, and sufficient 

 for our descriptions of the Caves, their nature and their position, is offered in the 

 following condensed description of M. d'Archiac's several Stages of the Cretaceous 

 System as it exists in the district under notice. 



Premier Etage. The uppermost group of the Cretaceous Limestones, coining out from under the Tertiary 

 heds on the Dordogne, and on the Ceuze at Beaumont and elsewhere, and spreading over the country to the 

 north-west, east, and south-east, are described by D'Archiac as being yellowish, sometimes soft and friable, 

 sometimes hard but full of small cavities, especially towards the upper part, where the stratification is often 

 indistinct, whilst the lower portion is more clearly bedded. Here and there the limestone is sandy with 

 grains of quartz and glauconite, and sometimes micaceous. 



These yellow limestones (" le Premier Etage " or " les Calcaires jaunes superieurs " of M. d'Archiac) 

 contain, among other fossils, Ostrea vesicularis, with Sphcerulites cylindraceus, and many other Rudistes. 

 These are large rough shells, peculiar to the Cretaceous rocks, often large, subcylindrical, rough externally, 

 coarsely cellular in structure, and known, according to the different genera, under the names of Uippuriies, 

 SpJicerulites, Radiolites, Caprina, &c. There are several zones or beds of Rudistes in the Cretaceous series 

 of the Dordogne, characterized by different species ; and the " Premier Etage," containing two beds of 

 them, is M. d'Archiac's " Upper Zone of Rudistes." 



The road-section on the hill of Beaumont, south of La Liude, showed, besides the overlying Tertiary beds 

 of limestone (of freshwater origin), sands, clays, and ironstone (altogether about 30 metres thick), a 

 succession of Cretaceous strata, 80 metres thick, in the following order (from above downwards) : 



1. Coarse-grained, friable, yellowish-grey limestone, with quartz grains in it. Containing some Rudistes 



(Sphcerulites, Radiolites, and Hippurites). 6 metres thick. 



2. Whitish cellular limestone, harder than the bed above. With numerous Rudistes (Sphcerulites and 



Radiolites). 10 metres. 



3. Hard limestone, passing into a yellow, compact but cellular and breccioid limestone. Cyclolites &c. 



15 metres. 



4. Yellow limestone, hard, subcrystalline, and fissile. 4 metres. 



5. Yellowish-white limestone, hard and subcompact, alternating with subcrystalliue limestone. 30 metres. 



6. Yellow homogeneous limestone, with earthy fracture, in regular beds. (This is the zone worked for the best 



building-stone in the line of quarries opened on both banks of the Couze and the Dordogne.) Towards 

 its base this rock becomes breccioid, hard, and yellowish-grey, with sparkling fracture. 15 metres. 



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