LECTURE X. 267 



bogs, reaching occasionally a thickness of thirty feet or more. 

 These peat moors have been distinguished as old and recent. 

 The old peat bed is said rarely to be more than one meter 

 thick. There are found in it in every direction trunks of alders, 

 oaks, firs, hazels, and bones, specially of the beaver and the 

 common bear. This old peat is in some spots covered with 

 sand dunes. It reposes upon a bed of sand and gravel resting 

 upon chalk, from which it is separated by a layer of brown or 

 black impervious marly clay. 



In our endeavours to decipher from the above description 

 the history of the valley of the Somme, we arrive at the con- 

 clusion, that this valley was excavated after the deposit of the 

 alluvia on the table land; that the terraces had at a later period 

 been formed by smaller streams, after which a temporaiy in- 

 crease of water in the streams caused these terraces to be 

 washed off, so that they are only preserved in certain spots ; 

 that the rolled gravel and the marly clay which now form the 

 bottom of the peat bogs, are the deposits of the waters which 

 scooped the valleys, after which the formation of the peat com- 

 menced. The formation, however, of the old peat in the vici- 

 nity of the sea has frequently been interrupted by the irruption 

 of the sea, which covered it with sand. 



The alluvial formations upon the platform correspond with 

 those which the Parisian geologists term diluvium des plateaux. 

 The lower bed of the terraces, with the pebbles, large blocks, 

 elephant bones, and flint implements, corresponds to the grey 

 diluvium of Paris (Biluviimi grisj ; the upper layer, with its 

 silicious sand and gravel, to the red diluvium of the French 

 (Diluviuin rouge) ; the brown layer to loam or loess. 



Must I repeat the touching story of how Boucher de Perthes, 

 a meritorious but somewhat eccentric antiquary of Abbeville, 

 first found the singular flints in the grey diluvium, how he 

 went with his discovery a-begging from door to door, and 

 found no hearing ; how, at length, some of his neighbours, and 

 next some Englishmen, became interested, until Amiens, Ab- 

 beville, St. Acheul, Menchecourt, and other locaHties of the 

 valley of the Somme became the resort of geological and archseo- 

 logical pilgrims, who visited these places either to be convinced 



