28 BELIQTJLE AQTJITANIC^E. 



sandstones belonging to the Trias (e), and exposes the underlying patches of Car- 

 boniferous strata (Coal &c., d) in its valley at Cublac and near Alassac*. 



The upper course of the Vezere is among the mica-schists, gneiss, granite, and 

 porphyries, or the metamorphic and igneous rocks (c, b, a), of the Central Plateau. 

 Hence the gravel along the river-course is composed of more or less rounded frag- 

 ments of quartzite and vein-quartz, and of micaceous, hornblendic, granitic, and 

 other rocks, derived from the uplands, mingled with the limestone and flint of the 

 lower district. Similar materials constitute the patches of the neighbouring old 

 Alluvia, formed at various times, when the river had greater breadth and a higher 

 level. 



The Granitic and Gneissic Rocks (a, b, c). The rocks constituting the higher 

 region, or Central Plateau, are chiefly "metamorphic," such as gneiss, marble, 

 slate, mica-schist, and other varieties of crystalline rocks, that have resulted from 

 the metamorphosis, or alteration by pressure, chemical agencies, or direct fusion, 

 of old sandstones, shales, limestones, &c., whether of Laurentian, Cambrian, Silu- 

 rian, or later age, into new forms of mineral matter, but often preserving clear 

 traces of their original bedding. Igneous rocks, such as greenstones, porphyries, 

 granites, &c., also occur as dykes and bosses protruding through these old schists ; 

 and mineral veins, or cracks filled with infiltrated quartz, metallic ores, and other 

 minerals, are of frequent occurrence. 



The Carboniferous Rocks (d). The Coal-measures consist of reddish schists, 

 sandstones, and conglomerates, yellowish-grey sandstones, and dark-coloured 

 micaceous shales with plant-remains (Ferns, &c.) and a few thin seams of coal ; 

 and they form isolated patches or remnants of a once broad sheet of Carboniferous 

 strataf. Resting against the old schists, they lie at high angles, and are con- 

 torted, dislocated, and traversed by porphyries. The red sandstones of the Trias 

 have been deposited on their upturned and denuded edges. 



The Triassic Rocks (<?). From near Alassac to L'Arche, and thence, past 

 Terrasson, to Le Lardin, the Vezere traverses red and variegated sandstones, 

 referred to the Triassic System, overlying unconformably some Carboniferous 

 strata, and capped here and there with patches of Infra-lias and Oolite. About 



* For a pictorial section of the hills of granite, gneiss, slate, coal-measures, and red sandstone, at Le 

 Saillant, near Alassac, see Dufrenoy and Elie de Beaumont's ' Explication de la Carte Geol. de la France,' 

 'vol. i. p. 126. 



t The sections of these heds at Alassac, Brives, Le Lardin, and Cublac are given in the ' Explic. Carte 

 Geol. de la France,' vol. i. pp. 126, 619, and 629. 



