^0 Miss M. 8. Johmton — Geological Notes on Ceniral France. 



« (lyke which has been buried in the scoria, projected from the 

 crater, of which every vestige has been obliterated. On the north 

 side of the Puy de Dome there is a curious sandy scoriaceous 

 deposit, containing small rounded grains and specular iron. The 

 grains are considered by M. Michel-Levy to be lapilli from the 

 volcano. Down the side of the Nid de Poule there is a large 

 (deposit of scoria and bombs of various forms. 



The Puy de Pariou is a scoriaceous cone, with an immense lava 

 stream of andesite flowing round the eastern side of the cone to the 

 basaltic plateau of Prudelles, which imposed so great a barrier that 

 the stream divided and flowed down to the Limagne plain on either 

 side of the plateau. Between Puy de Pariou and Prudelles, at 

 Le Cressigny, a cordierite gneiss may be found, while the Pliocene 

 basalt of Prudelles contains zeolites. 



Proceeding from Royat by train to La Bourboule, the confines of 

 Mont Dore massif are entered upon. The line runs round the north 

 •of the Monts Domes. At Volvic a fine andesitic stream is crossed ; 

 ■this stone is much quarried for building purposes, whose durable 

 ■qualities are well seen in the cathedral ot Clermont Ferrand. 



On arriving at La Bourboule, the first section of interest is at 

 .a short distance from the station at Lusclade, where rhyolites, 

 .perlites, phonolites, and trachytes are found. One section of rhyolite, 

 ■facing the road to Mont Dore and at a small gorge, shows remarkable 

 •stratification, the rhy'olite being of two kinds, glassy and fibrous. 

 Up the gorge the rhyolite becomes perlitic, and masses of ophitic 

 basalt from the heights above have fallen into the bed of the stream. 

 Phonolites without nepheline, with nosean and haiiyne, are found 

 a few 3'ards further to the south. 



The district of Mont Dore is formed by two principal centres 

 of eruption — one at the Pic de Sancy, the other between the 

 .Banne d'Ordenche, Puy de la Croix Morand, and Puy de I'Angle, 

 overlooking the gorge mentioned above. The Pic de Sancy is 

 trachytic, and fine porphyroidal trachyte may be found on its 

 inorthern slopes. In the ravines of the Grande Cascade and 

 Egravat remarkable sections are seen, tuffs and conglomerates of 

 i:rachyte or andesite alternating with compact flows of different 

 rocks, as trachytes, andesites, basalts, and labradorites.^ The greater 

 part of the massif is formed of materials of every size from fine 

 cinerites to conglomerates. 



Cinerites containing vegetable remains are well exposed on the 

 west side of the valley of the Dore, to the north-west of Mont Dore 

 Jes bains. At the Kavin de la Grande Scierie is an interesting- 

 example of denudation and successive volcanic phenomena. The 

 ibottom of the ravine is of cinerite, which rises on either side and 

 iis capped by porphyritic trachyte. x\fter the first erosion of the 

 valley a stream of lava poured down it, partly filling it, and which 

 was in its turn eroded and has left its mark in a bank of andesite on 

 both sides of the ravine. A little further on is a basaltic dyke rising 



^ A labradorite of French geologists is a basic andesite of English geologists. 



