64- Miss M. S. Johnston — Geological Notes on Central France. 



latter is so abundant that it is called ' le pays des phonolites,' and 

 the rock gives a characteristic appearance to the landscape (PI. Ill, 

 Fig. 4). Some of the best sections for obtaining it are at Lardeyrol,. 

 specimens without nepheline ; at Mont Pidgier, containing a vast 

 quantity ; at Boussoulet and Montvert, a phonolite rich in nepheline 

 and EBgyrine; near Estables the ' rocher d'Aiglet'; and the Mezen 

 peak itself is mainly composed of this rock. 



On the road from Le Puy to Blavozy are several excellent 

 sections of arkose of Eocene age and Oligocene sandy clays and 

 spotted marls, while at Blavozy itself there is a very large deposit 

 of arkose, in which great crystals of orthoclase from the older 

 granite appear. At Queyrieres is found a good Miocene trachyte. 



There are a few glacial lakes in this district, the chief one being 

 that of St. Front, crater-form in shape and worn in the basalt. 



Large crystals of orthoclase and hornblende can be picked up 

 in the labradorite tuffs of Besseyre, many of the hornblende crystals 

 being very nearly perfect in shape. Between Coubon and Le Puy 

 may be noticed the lava streams from the Mont Jonet of Quaternary 

 age, overspreading those of the Garde d'Ours, which was an active 

 volcano in Pliocene times. 



- The geologist may now, if he chooses, pass from the land formed 

 by the internal fires to that deposited in the waters, by driving 

 from Le Puy to Mende, a distance of ninety-two kilometres. One 

 first traverses igneous and metamorphic rocks as far as Mont Lozere, 

 at which point the Liassic and Jui'assic plateaux are reached, and 

 where the road makes a rapid descent into the valley to Mende. 



The rocks to be noted en route are first the bombs containing 

 peridotite found in a cone at Tarreyre. Basaltic plateaux are 

 crossed until one arrives at Langogne. The hills on the west 

 side of the valley of the Allier are of porphyritic granite; here 

 the felspathic crystals of orthoclase are very large. 



From Chateauneuf de Kandon one perceives the Gausses, of 

 Secondary age, rising against the crystalline mass of Mont Lozere. 

 The Gausses are immense undulating barren plateaux of limestone 

 of Jurassic age. There are frequent depressions called ' sink-holes,' 

 and the whole country from Mende to the Gevennes on the south 

 is supposed to be riddled with caverns ; some with underground 

 streams, as at Bramabiau and Padirac, others, where there is an 

 entire absence of running water and where they are slowly filling 

 with stalactitic materials, as at Dargilan, 



PI. IV, Fig. 5 is a view taken from the pathway up to Dargilan, 

 the entrance of the cave being at the top of the cliffs in Middle 

 Jurassic dolomitic limestone ; the rounded formation on the top 

 of the precipitous cliff is of Kellaway age. The Gausses are also 

 cut up by caiions, that of the Goi'ge de Tarn being the largest. The 

 river of this gorge is fed by underground springs, and its sides 

 are weathered out into pinnacles and buttresses. 



In the Dourbie gorge, not far from Milhau, is Montpellier-le- 

 Vieux. The limestone on the top of the Gausse Noir has been worn 

 away either bv weathering or, as some think, by underground! 



