ST. ACHEUL. 363 



tinuous, but now generally presenting numerous interruptions. 

 A more magnified view of the strata at St. Acheul, near 

 Amiens, is shown in fig. 202. The upper layer of vegetable 

 soil having been removed, we have 



1. A bed of brick earth (a), from four to five feet in thick- 

 ness, and containing a few angular flints. 



2. Below this is a thin layer of angular gravel (&), one to 

 two feet in thickness. 



3. Still lower is a bed of sandy marl (c), five to six feet 

 thick, with land and freshwater shells, which, though very 

 delicate, are in most cases perfect. 



4. At the bottom of all these, and immediately overlying 

 the chalk, is the bed of partially rounded gravel (d) in which 

 principally the flint implements are found. This layer also 

 contains many well-rolled tertiary pebbles. 



In the early Christian period this spot was used as a ceme- 

 tery : the graves generally descend into the marly sand, and 

 their limits are very distinctly marked, as in fig. 202/; an 

 important fact; as showing that the rest of the strata have lain 

 undisturbed for 1500 years. Some of the coffins were of hard 

 chalk (fig. 202 e), some of wood, in which latter case the nails 

 and clamps only remain, every particle of wood having perished, 

 without leaving even a stain behind. Passing down the hill 

 towards the river, all these strata are seen to die out, and we 

 find ourselves on the bare chalk ; but again at a lower level 

 occurs another bed of gravel, resembling the first, and capped 

 also by the bed of brick earth which is generally known as 

 loess. This lower bed of gravel is that called by Mr. Prestwich 

 the lower-level gravel. 



These strata, therefore, are our witnesses; but of what? 

 Are they older than the valley, or the valley than they ? Are 

 they the result of causes still in operation, or the offspring 

 of cataclysms now, happily, at an end ? 



If we can show that the present river, somewhat swollen, 



