62 THE ANTIQUITY OF MAN 
to reach the Aurignacian period ; how long, we can but 
dimly perceive at present. The formation of a deposit, 
30 feet deep at Solutre, must have occupied a long space 
of time. The process of its formation is revealed by 
M. Arcelin's section. The great block of stone and the 
rocky debris which lie in the strata between the layers 
containing the ancient hearths have been detached from 
the face of the adjacent hill, as its exposed face weathered 
under the frost, the wind, and the rain. The debris thus 
detached from the hill tended to drift down the slope in 
times of rain, snow, and flood, gradually covering and 
burying the human habitations, and sealing them up 
as historical records. The climate has changed since 
Aurignacian times, for the Palaeolithic cultures lie within 
what is regarded as the Ice age, but which it is better to 
speak of as the Pleistocene epoch. We know from the 
kind of animals which live in the Aurignacian period that 
the climate was milder than in the Magdalenian age. 
Indeed, we shall see later that the last of the glacial 
phases occurred when the Magdalenian culture was at 
its height. 
Before returning to England to apply the knowledge 
we have gained from our tour in France, there are two 
other classical sites which demand our attention. Neither 
at Mas d'Azil nor at Solutre, abundant as the traces of 
Palaeolithic man were, did we find the men themselves. 
To supply this blank in our knowledge we must glance 
at the remarkable discoveries made in the caves situated 
in cliffs along the French coast of the Mediterranean. 
A little over a mile to the east of Mentone, just beyond 
the French frontier, the red rocks of Grimaldi rise from 
the sea. The caves, where ancient man made a home, 
open on their southward face about 60 or 70 feet above 
the level of the sea. A terrace made along the foot of 
the cliffs serves as a highway between France and Italy. 
Indeed, many of the caves open just above the road. 
In 1872, M. Emile Riviere discovered remains of ancient 
man in some of the Grimaldi caves. Further discoveries 
were made subsequently, and disputes arose as to their 
