INTERGLACIAL EPOCHS. 



3i9 



circumference of 27 metres. He states also that fragments a 

 cubic metre in volume may be counted by thousands. All the 

 stones, large and small alike, are angular, and many are covered 

 with glacial striae. They are scattered pell-mell, higgledy-piggledy, 

 through the tuff-like loam in which they occur, and in places 

 where they are closely aggregated irregular cavities occur between 

 the blocks, showing that the stones were rudely heaped and piled 

 up in the same manner as the debris of a moraine. The fragments 

 consist of many different kinds of rock, such as granite, trachyte, 

 basalt, and Miocene limestone, all of which have been derived 

 from Mont Dore and the adjacent neighbourhood. The only rock 

 of the district which is not represented in the " conglomerate " is 

 the modern lava of Montchalm. On the other hand, some stones, 

 the parent rock of which is unknown in place, occur in consider- 

 able numbers. Such are blocks of a peculiar pumice which 

 abound at Perrier, and fragments of certain trachytes and con- 

 glomerates. There can be no doubt, however, that all these 

 belong originally to Mont Dore, the beds of which they once 

 formed a portion having been destroyed by the glacier which 

 transported the debris to its present position. The largest blocks 

 that occur in this remarkable glacial accumulation are all 

 trachytes which have travelled from Mont Dore, a distance of 25 

 kilometres. 



The so-called conglomerate is, as Julien has shown, nothing 

 more nor less than the moraine profonde of a glacier that formerly 

 descended from Mont Dore ; it is, in short, a " boulder-clay." 

 Two irregular beds of water-worn stones are intercalated in the 

 mass, and these separate it into three successive sheets. Accord- 

 ing to Julien, these pebble-beds testify to the action of torrential 

 waters, and to epochs when the glacier receded and allowed 

 water to denude and rearrange the materials of its bottom- 

 moraine. Underneath the whole mass are found the relics of an 

 old forest. 



This glacier must have continued to occupy its ground for a 

 long time, to judge from the thickness and the extent of its 

 moraine profonde, but eventually it melted away, and by and by 



