E. Andrews on Human Antiquities at Abbeville, &c. 189 
layers deposited since the Roman conquest, is to the quantity 
in the whole cone, so is the time required for the deposit of 
these layers, to the time required for the formation of the whole 
cone, 
The revised data and calculation would be as follows. The 
lower cone is really a half cone, the apex resting against the 
declivity of the upper one, and the base being a semicircle, 
The dimensions are nearly as follows: 
Height of apex, 38 feet. 
Radius of the base, feet. 
Cubic feet in the strata deposited since the Roman con- 
quest, 5,283,205, 
Time of deposition of the same, 1,300 to 1,500 years. 
Cubic feet in the whole lower cone, 16,116,408. 
Time of deposit of the same, 3,965 to 4,576 years. 
_ Adding the 300 years, which have elapsed since the deposit 
ceased, the present age of the lower cone would be from 4,265 
to 4,876 years, 
It will be noticed that this is not far from the age which we 
estimated for the peat beds of the Somme. It would seem, 
therefore, that the period of higher water, which preceded both, 
was simultaneous at the two places. 
The calculations respecting the upper and larger cone are 
vitiated not only by the overestimate of the age of the lower, . 
on which that of the upper depends, but still more by leaving 
out of view several important geological facts. | 
__ The amount of gravel transported by a torrent, depends on 
the amount of water in it. Or, in other words, upon the annual 
rainfall. It is important to inquire, therefore, into this point. 
The fact that at the same period the river Somme had an im- 
mensely greater volume of water than now, and the water of 
Lake Geneva stood fifty feet above its present level, gives a 
 eeue! that the torrent of the Tinitre would be found af- 
ected by the same causes as the lake and the river. The ex- 
amination of the upper cone itself settles this question, for it 
carries its history in the channels on its surface. The gravel 
cones of the Alps are marked with channels of a size propor- 
tioned to the quantity of water which flows in them, because 
the stones and gravel are left on each side of the water course 
up to high water mark, showing the exact size of the stream. 
As the gravel accumulates it gradually raises the bed of the 
torrent above the rest of the cone, until the water breaks through 
now on this side and now on that, and distributes its gravel 
over the lower portions. Hence the comparison of the torrent 
channels of the two cones, will show the size of the stream 
1ich formed them at the two periods. Now the bed of the 
