8 



■of the Somme was always gained l)y the simple fracture of the 

 flint, and by the repetition of man}' dexterous blows. Some of 

 these tools were probably used as weapons, both of war and of 

 the chase, others to grub up roots, cut down trees, and scoop out 

 canoes. Between the spear-head and oval shapes there are 

 various intermediate gradations, and there are also a vast 

 variety of very rude implements, many of which may have been 

 rejected as failures, and others struck off as chips in the course 

 of manufacturing the more perfect ones. To describe without 

 the aid of diagrams the structure of the alluvial deposits in the 

 valley of the Somme, in which these implements are found, is 

 not so simple a task as to describe the implements themselves. 

 I will however l)rietly endeavour to make clear the main features. 

 The chalk hills \rhich l)ound the valley are two or three hundred 

 feet in height The masses of drift or alluvium lie in the 

 bottom of the valley, and on the sides of the hills For the 

 sake of proceeding from the known to the less known, Lvell 

 makes his surve}' of these deposits retrospective, and beginning 

 Avith the most recent, proceeds backwards to the more ancient. 

 Of all these geological monuments, the most recent is the peat. 

 This substance occupies tlic l)ottom of the valley from some 

 miles inland to the sea. It is in places thirty feet tliick. All 

 the embedded mannnalia and shells are recent and belong to 

 species now inhahiting Eui-ope. Gallo-Iioman works of art are 

 foun'l in the peat near tlu- surface, and at a greater depth, 

 Celtic weapons. ]3ut the dei)th at which Komiui works of art 

 occur, varies in ditferent places, and is no sure test of age : 

 because in some parts the peat being tluid, heavy substances 

 sink ill it from their own gravity In one <-as(! ]\[. de Perthes 

 found several large flat dishes of rioman pottery, which, 1> in-- 

 in a horizontal position, were prevented from sinkhig through 

 the underlying peat. Allowing about fourteen centuries for the 

 growth of the superineiimbeiit matter, he calculated that thv, 

 thickness jfained in a hundied years would be no more than 



