yune 22, 1876] 



NATURE 



179 



part in its circulation as salt does in that of the ocean. In con- 

 clusion, I would say, look at the isotherms between 65° 42' S., 

 and 50° 1' S. published in Report No. 2 of the Challenger. 

 May 10 Dig BY Murray 



ANCIENT GLACIERS IN AUVERGNE 

 TT AVING just returned from Auvergne, where I have 

 •*- -*• been searching for the tracks of former glaciers 

 among the old volcanoes of the Monts Dome and Mont 

 Dore, 1 send a few notes to Nature, in the hope that 

 they may prove useful to other geologists who may explore 

 that most remarkable and interesting country during the 

 ensuing summer. My companions were three members 

 of the Cotteswold Naturalist's Field Club, Sir W. V. Guise 

 (the President), Sir David Wedderburn, and Mr. Lucy, all 

 well versed in the phenomena presented by glaciation. 



With regard to the Monts Dome and the country round 

 Clermont Ferrand, it is evident that no glaciers have 

 occupied the vales since the outpouring of the later lava 

 currents, and the volcanic outbursts of the craters of the 

 Puys de Dome ; and yet, as I have already mentioned in 

 the pages of Nature, M. Le Coq discovered remains of 

 the Mammoth, Tichorhine rhinoceros, and Spermophilus, 

 which had been washed into drifts and fissures in the most 

 recent lava currents of Volvic and Gravenoire near Beau- 

 mont. Such drifts deserve especial attentioti, as they appear 

 to owe their origin to a period when there was greater trans- 

 portation of angular and subangular debris by rain- wash 

 and melting snow, or neve, than there is at present. It 

 may have been during this period that the northern 

 animals became inhabitants of Central France. Such 

 angular and sub-angular drifts may be seen in various 

 localities as in the road which descends from the south 

 side of Gergovia, between the village of Merdogne and 

 the high road to Clermont Ferrand, and again at the 

 base of the Puy Dallet, where the high road descends to 

 the village of Dallet, and atmospheric drifts are seen to 

 overlie the old river shingle of an ancient Allier. The 

 geologist who examines the source of the old basaltic 

 current which Mr. Scrope believes to have flowed from 

 the Puy de Berz^, near St. Genest de Champanelle, and 

 to have extended over the freshwater strata of Gergovia, 

 may learn a good lesson as regards the deceitful appear- 

 ances of glaciation often set up by granitic rocks. Most 

 of the country between Ceyrat, near Mont Rognon, and 

 Theix looks regularly " moutoneed," and may mislead 

 anyone who has not become convinced, by careful exami- 

 nation, that this appearance is owing to atmospheric 

 weathering, and the desquamation of the granitic rocks 

 which separate at the joints and weather into rounded 

 boulders assuming sometimes the aspect of blocs perches. 

 There are no signs of glaciation, however, among the 

 older basalts which overlie the granite rocks, in so many 

 localities, and which ought to show it if glaciation there 

 had been. 



In the country of the Monts Dore the evidence is most 

 puzzling, and in some respects contradictory. Arrived at 

 Monts Dore des Bains we searched carefully for glacier 

 evidences in the valley of the Dordogne and the gorges 

 de I'Enfer and de la Cour, and though some of the knolls 

 are rounded, and there is a vast amount of debris from the 

 rocks around and above, nowhere could we see signs of 

 true moraines, perched blocks, or the usual evidences of 

 glacier action ; and certainly the position of the masses 

 of rock called " Les Trois Diables," which I believe are 

 by some set down as blocs perches, are far too close to 

 the rocks in situ to allow us to attribute their trans- 

 portation to a glacier rather than to a fall from the 

 precipices above. They belong to the " Chemins du 

 Diable," which are preparing for a similar descent. 

 Again, and I must here state that I arrived at conclu- 

 sions contrary to those of my friends, I believe that a 

 glacier has descended, in long ago ages, down the valley 

 of the Dordogne, but so long since that the vast masses 



of debris which have fallen from the rocks which skirt the 

 valley, combined with the wear and tear of atmospheric 

 agencies, the constant shifting of the bed of the Dordogne 

 and its hundreds of tributary rills which during the 

 melting of the snows everywhere wash, roll, wear, and 

 transport the ddbris of the vale, all have assisted in 

 destroying and masking any glacier evidence there may 

 have been in past limes. I was led to this conclusion from 

 the examination of the higher ground, and the detection 

 of v/hat I believe to be moraine matter and transported rock 

 masses, on the road between Mont Dore des Bains and 

 Latour, as on the platform below the Rochers de Beauzac, 

 &c. 



The Tranteine valley, where Dr. Hooker discovered 

 the transported rock-masses and which he has already 

 described in Nature, lies at right angles to the 

 Dordogne valley, runs due south, and faces the Cantal. 

 It is difficult to understand why glacier rehcs should be 

 preserved in this valley and none in that of the Dordogne. 

 This difficulty, however, vanishes somewhat when surveying 

 the difference in the contour of the ground, the difference in 

 the watershed of streamlets, and the low hill against which 

 the great rock-mar.ses are stranded, consisting of moraine 

 matter overlying beds of basaltic lava. The Tranteine 

 valley may be reached by passing over the Col between 

 the Pic de Sancy and Puy Ferrand, and turning down 

 the gorge to the south, or by the long roundabout route 

 through the village of Latour. We selected the former 

 for our first attack, taking the Latour route two days later. 

 I would here recommend as guide, Guillaume Pierre, of 

 the Hotel Chabourg aind, to whom I pointed out certain 

 phenomena on descending the gorge, which I think are 

 worthy of notice. I also recommend no one to attempt 

 this route who is not a good walker — " Facilis descensus," 

 &c. The transported rocks, one of which Dr. Hooker 

 sketched, lie stranded in moraine matter, which again 

 rests on beds of black basalt, as may be seen at the little 

 waterfall of the Tranteine stream. The rocks themselves 

 come from the Pic de Sancy, and consist of what Scrope 

 calls " porphyritic trachyte," but perhaps now they may 

 be termed a granitic felstone or a felstone porphyry. Dr. 

 Hooker calls them domite, but this term is now usually 

 applied to the white, light, pulverulent rock like that of 

 the Puy Sarcoui in the Puys de Dome. On the right 

 and left of the transported rocks the hills are rounded, 

 and blocs perches are seen resting on them. There 

 is a fine section on the Tranteine stream, en route to 

 Picherande, where large transported rock-masses may be 

 seen resting on glacial till. Following the valley down to 

 the bridge which crosses the Tranteine river between 

 Latour and Picherande, the observer will find rounded 

 surfaces and transported moraine matter, but a vast deal 

 of atmospheric weathering has gone on since the days 

 when the ice passed away. 



Travelling down the valley of Besse to Lake Pavin, I 

 thought I recognised glacier action; and again at the head 

 of the valley of Chambon ; but if glaciers ever flowed 

 down these valleys, it is evident that they must have done 

 so before the eruption of the Puy de Tarlaret or the Puy 

 d'Eraignes. The occurrence of the volcanic cone of Tar- 

 taret right in the middle of the valley of Chambon is fatal 

 to the supposition that a glacier of any size ever came 

 down from the mountains since the outburst of the 

 cinders and lavas of Tartaret. 



If, therefore, after three visits to the volcanic regions of 

 Central France 1 may be permitted to give a broad view 

 as to the time when glaciers swept down the valleys of 

 Mont Dore, I should say that it was in days of old, 

 when the Alpine glaciers reached the Jura, and the Rhine 

 glacier swept over to the plains of Bavaria, when there 

 were glaciers in the Vosges and in the Black Forest ; and 

 that when those ice rivers melted and passed away, so also 

 did the glaciers of Mont Dore. W. S. Symonds 



Ptndock Rectofy, Tewkesbury, June ^ 



