122 SECTION OF STRATA AT MENCHECOURT. CHAP. Till. 



ing pit some minoi" variations in the nature and thickness of 

 the superimposed deposits maybe seen, tliere is yet a general 

 approacla to uniformity in the series. The only stratum of 

 which the relative age is somewhat doubtful is the gravel 

 marked a, underlj'ing the peat, and resting on the chalk. It 

 is only known by borings, and some of it may be of the same 

 age as No. 3; but I believe it to be for the most part of more 

 modern origin, consisting of the wreck of all the older gravel, 

 including No. 3, and formed during the last hollowing out 



Fig. 16 



Somme.R 



Chalk 



Section of fluvio-marine strata, containing flint implements and bones of extinct 

 mammalia, at Menchecourt, Abbeville.* 



1 Brown clay with angular flints, and occasionally chalk rubble, unstratified, 

 following the slope of the hill, probably of subaerial origin, of very varying 

 thickness, from two to five feet and upwards. 



2 Calcareous loam, buff-colored, resembling loess, for the most part un- 

 stratified, in some places with slight traces of stratification, containing 

 fresh-water and land shells, with bones of elephants, <fec. ; thickness about 

 fifteen feet. 



3 Alternations of beds of gravel, marl, and sand, with fresh-water and land 

 shells, and, in some of the lower sands, a mixture of marine shells ; also 

 bones of elephant, rhinoceros, <fec., and flint implements; thickness about 

 twelve feet. 



a Gravel underlying peat, age undetermined. 



h Layer of impervious clay, separating the gravel from the peat. 



and deepening of the valley immediately before the com- 

 mencement of the growth of peat. 



The greater number of flint implements have been dugout 

 of No. 3, often near the bottom, and twenty-five, thirty, or 

 even more than thirty feet below the surface of No. 1. 



« For detailed sections and maps of this district, see Prestwich, Philosophical 

 Transactions, 1860, p. 277. 



