34 RELATION OF THE RUBBLE-DRIFT 



animals, those of the Mammoth preponderating in the 

 lower, and those of the Eeindeer being more abundant 

 in the upper beds, where they are associated with 

 a larger number of the worked flints of Palaeolithic 

 Man. Overlying all these beds was a mass of 

 debris from the rocks above, which masked the Cave 

 deposits in the same way that the Head masks the old 

 cliffs of the Channel. Eesting on the top of this rubble, 

 there is occasionally a layer of debris containing the 

 stone implements of Neolithic Man, together with 

 the remains of Horse, Ox, Reindeer, and other recent 

 species, as also of several recent species of birds. 

 The position of these caves is indicated generally in 

 the diagram, Fig. 3. 



FIG. 3. Diagram-Section across a Valley in the Ardennes, showing the 

 relative position of the Caves (or Rock-Shelters), of the angular Rubble- 

 drift, and of the Loess. 



Carboniferous and Devonian Rocks 



(a) Level of the river at the time of the erosion of rock-shelter or Cave 

 No. 1. 



(6) Level at the subsequent period, when Cave No. 2 was formed. 



The tale that these caves tell is this : At the date 

 of No. 1 Cave the river had excavated the valley to 

 the depth of the line a. The work of erosion con- 

 tinuing, another cave was formed on the level of b % 

 to which we will confine our attention. On the ledge 

 worn out on the level of b, the old river deposited a 

 layer of rounded pebbles, carried down by the stream 



