152 
ELEMENTS OF GEOLOGY. 
4'. Sometimes the valley-gravels of older date are entirely 
missing, or there is only one, and occasionally there are more 
than two, marking as many successive stages in the excava¬ 
tion of the valley. They usually occur at heights varying 
from 10 to 100 feet, sometimes on the right and sometimes 
on the left side of the existing river-plain, but rarely in great 
strength on exactly opposite sides of the valley. 
Among the genera of extinct quadrupeds most frequently 
met with in England, France, Germany, and other parts of 
Europe, are the elephant, rhinoceros, hippopotamus, horse, 
great Irish deer, bear, tiger, and hyaena. In the peat, No. 1 
(Fig. 87), and in the more modern gravel and silt (No. 2), 
w’orks of art of the ages of iron and bronze, and of the later 
or Neolithic stone period, already described, are met with. 
In the more ancient or Paleolithic gravels, 3 and 4, there 
have been found of late years in several valleys in Ih*ance 
and England—as, for example, in those of the Seine and 
Somme, and of the Thames and Ouse, near Bedford—stone 
implements of a rude type, showing that man coexisted in 
those districts with the mammoth and other extinct quadru¬ 
peds of the genera above enumerated. In 1847, M. Boucher 
de Perthes observed in an ancient alluvium at Abbeville, in 
Picardy, the bones of extinct mammalia associated in such a 
manner with flint implements of a rude type as to lead him 
to infer that both the organic remains and the works of art 
were referable to one and the same period. This inference 
was soon after confirmed by Mr. Prestwich, who found in 
1859 a flint tool in situ in the same stratum at Amiens that 
contained the remains of extinct mammalia. 
The flint implements found at Abbeville and Amiens are 
most of them considered to be hatchets and spear-heads, and 
are different from those commonly called “celts.” These 
celts, so often found in the recent formations, have a more 
regular oblong shape, the result of grinding, by which also 
a sharp edge has been given to them. The Abbeville tools 
found in gravel at different levels, as in Nos. 3 and 4, Fig. 
87, in which bones of the elephant, rhinoceros, and other 
extinct mammalia occur, are always unground, having evi¬ 
dently been brought into their present form simply by the 
chipping off of fragments of flint by repeated blows, such as 
could be given by a stone hammer. 
Some of them are oval, others of a spear-headed form, 
no two exactly alike, and yet the greater number of each 
kind are obviously fashioned after the same general pattern. 
Their outer surface is often white, the original black flint 
having been discolored and bleached by exposure to the air. 
