358 The American Geologist. December, i89^ 
vation, it is not known whether they contain stone implements 
and fossil bones; but generally, according to Ladriere. these 
are absent or rare in the highest beds of the valley gravels 
throughout northern France. In the vicinity of Montiers. 
one to two miles northwest of Amiens, nine gravel pits, con- 
taining worked flints and bones of extinct animals nearly as 
at St. Acheul. are shown by Tylor's description and map to 
range in hight from yj to 155 feet above the sea, or from 17 
to 95 feet above the Somme, the upper limit of the excava- 
tions being the same in relation to the river as near St. Acheul. 
The distinction of upper and lower gravel deposits, which 
Prestwich and Lyell made prominent in their writings, was 
]ironounced by Tylor, as it seems to me with sufificient rea- 
sons, to be seldom definitely observable, the series, where 
developed at considerable bights, being usually continuous 
thence down nearly or quite to the bottomland and river. 
Ladriere, who in 1875 and ensuing years has extensivelv 
examined and described the Pleistocene valley deposits of the 
Seine, Somme, and other river basins of a wide region ex- 
tending northward into Belgium, divides these deposits into 
three somewhat similar series, successive in age and strati- 
graphic order, each of which can be traced from the bottoms 
of the valleys up to the plateaus, though not to their greatest 
bights. These series, each consisting of a regular sequence 
of gravel, sand, loam or loess, etc., representing three dis- 
tinct stages of the Pleistocene period, are doubtless to be 
correlated with stages of advancing glaciation, interrupted by 
times of decrease and recession of the European ice-sheet. 
The researches of Ladriere thus present a record of climatic 
changes south of the glaciated area, by which geologists may 
very satisfactorily connect the evidences of primitive man 
in France with the time divisions of the Glacial period. His 
detailed notes of each of the three Pleistocene series and 
stages recognizable in these valleys are fully quoted bv 
Prof. James Geikie in the third edition of the "Great Ice Age" 
(1894, pp. 630-632), from which it appears that flint imple- 
ments of the Acheulian or Chellean type occur throughout 
the lower series; that such implements are also found in the 
middle series, but probably, as Ladriere thinks, through de- 
rivation from the older and stratigraphically lower beds; and 
