Primitive Ma?t in the Somme Valley. — Upha?n. 353 
lutre in Burgundy; and 4, Magdalenian, from the caves of La 
Madeleine in Dordogne. These time divisions are character- 
ized by increasing variety and excellence of the implements 
made, and by concomitant changes of the fauna. The imple- 
ments found in the Somme valley are referable only to the 
earliest stage, which had at first a mild and moist climate, 
changing afterward to severe cold, with thick ice on the rivers 
in winter, broken and floating large blocks of rock in spring. 
Let us now examine the geologic origin and deposits of this 
valley in their relation to these stages of archgeologic develop- 
ment, comparing both records with the ascertained history of 
the Ice age in the British Isles and northern Europe, and with 
estimates of its duration and that of the Postglacial period. 
Above Amiens the Somme basin . has been eroded to an 
undulating surface of broad but low hills and ridges, and is 
drained by several streams which converge in and near that 
city, being the sources of the supply of the Pleistocene gravels 
extensively excavated at St. Acheul, St. Roch and Montiers. 
which are situated respectively in the southeastern, western, 
and northwestern environs of the city. From Amiens to the 
sea the valley is troughlike, with a bottomland from a half mile 
to a mile and a half in width, down to Abbeville, and thence 
widening to three or four miles at its mouth, inclosed usually 
by very gentle or moderately steep slopes, but in a few places 
bordered by a steeper or precipitous bluff formed through di- 
rect undermining by the river at some time during the slow 
process of the valley erosion. 
The river at Amiens is about 65 feet above the mean tide 
sea level; at Montiers, 58 feet; and at Abbeville, about 15 feet, 
the high tides having formerly reached above the city, until 
held back by the engineering improvements of the river course 
which now restrict its once meandering and dividing waters 
to a single straight canal along its next nine miles. The bot- 
tomland is mostly no more than two to five feet, and in its 
highest parts about ten feet, above the river in its ordinary 
low water stage. Along nearly all the distance below Amiens, 
it has large tracts of peat, from 10 to 30 feet in depth, thus 
extending far beneath the level of the river, or even, in the 
vicinity of Abbeville, beneath the sea level. During many 
centuries the peat has been excavated for fuel, and many 
