Primitive Man in the Somme Valley, — Upharn. 357 
marginal parts of these deposits have been later carried away 
by the undermining action of the streams which brought them 
or of the main river. Along the Connecticut river a wide 
flood plain of modified drift was built up, filling the valley, 
to the level of the highest continuous terraces, 100 to 200 
feet above the river; and the terraces are remnants of that 
flood-plain and of the lower temporary levels occupied and 
abandoned by the river during its process of rem-oval of the 
greater part of that original deposit of the modified drift. 
x\bove the highest terraces of the main Connecticut valley, 
however, some of its tributaries, exceptionally supplied wdth 
drift from the drainage of the contiguous receding ice-sheet, 
formed lateral deposits, terrace plains and alluvial fans, as at 
North Haverhill and in other places south to Hanover, N. H.. 
ranging in hight from 40 to 250 feet above the valley terraces, 
analogous in their mode of deposition with the Somme 
gravels."^ In the Somme valley the supply of material was less 
than that set free from the melting North American ice-sheet, 
and it was insufficient to build up a flood-plain in any part 
of this valley below Amiens, though at many places it formed 
extensive deposits on either side, which sometimes reach, with 
slopes nearly like those inclosing the valley, from the bot- 
tomland up to hights of 50 to 100 feet; and patches of sim- 
ilar gravel and sand occasionally are observable also at greater 
hights, nearly to the verge of the uplands. 
Levelling done for Mr. Alfred Tylor by the railway en- 
gineer, M. Guillom. gave the altitudes of the bottom and the 
original surface of the large St. Acheul gravel pits (two are 
each a quarter of a mile long), the richest in flint hatchets 
among the numerous excavations in and near Amiens, as 
respectively 140 and 160 feet above the sea, or about 75 and 
95 feet above the river, which is a half mile distant to the 
north. The pits are not at the upper limit of the gravels, for 
Tylor remarks that "the sections near Amiens show the val- 
ley-gravel continuous from a height of 200 feet, at St. Acheul 
* * * to the River Somme (coated over by a nearly uni- 
form warp of loess), and laid at a low gradient not exactly 
parallel to the surface of the chalk, but rather in its concav- 
ities." These higher gravel beds, however, having no exca- 
*Geology of N. H., vol. Ill 1878, pp. 29-38, with maps and sections. 
