252 ORIGINAL ARTICLES. 



Fig. 4, gives a section across the valley of the Somme at 

 Abbeville, taken from Mr. Prestwich's first paper.* "We shonkl 

 get almost the same arrangement and position of the different beds, 

 not only at St. Acheul, but elsewhere along the valley of the Somme, 

 wherever the upper beds have not been removed by subsequent 

 action of the river. Even at St. Valery, at the present mouth of 

 the river, we found a bed of gravel at a considerable height above 

 the level of the sea. This would seem to show that at the period of 

 these high level gravels, the channel was narrower than it is at 

 present, as indeed we know to have been the case even in historical 

 times. So early as 1605 our countryman Versteganf pointed out 

 that the waves and tides were eating away our coasts. Sir C. 

 Lyell gives much information on this subject, and it appears that 

 even as lately as the reign of Queen Elizabeth, the town of Brighton 

 was situated on the site now occupied by the Chain Pier. 



Mr. Prestwich has showai+ that a section, similar to that of the 

 Somme, is presented by the Lark, Waveney, Ouse, &c. while it is well 

 shown also along the banks of the Seine. Probably, indeed, it holds 

 good of most of our rivers, that along the sides of their valleys are 

 patches of old gi-avels left by the stream at various heights, before 

 they had excavated the channels to their present depth. Mr. Prest- 

 wich considers that the beds of sand and gravel can generally be 

 divided into two more or less distinct series, one continuous 

 along the bottom of the valleys and rising little above the water 

 level ; the other occurring in detached masses at an elevation of 50 

 to 200 feet above the valley. Eather, perhaps, these are the two 

 extremes of a series, once continuous, but now almost always pre- 

 senting some interruption. A more magnified view of the strata at 

 St. Acheul, near Amiens, is shoA^ai in Fig. 2. The upper layer of 

 vegetable soil ha\Tng been removed, 



1. A bed of brick earth from four to five feet in thickness, 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, five to six feet thick, with 

 land and fresh water shells, which though very delicate, are in most 

 cases perfect. 



4. At the bottom of all, and immediately overlying the chalk, is 

 the bed of subangular gravel in which the flint imj)lements are found. 



In the eai'ly Christian period this spot was used as a cemetery : 

 the graves generally descend into the marly sand, and their limits 

 are very distinctly marked, Fig. 2 ; an important fact, as showing 

 that the rest of the strata have lain undisturbed for 1500 years. 

 The coffins used were sometimes made of hard chalk, sometimes of 

 wood, in which latter case the nails and clamps only remain, every 



* Phil. Trans. 1800. f See Principles of Geologv, p. 315. 



t Proc. Roj. Soc. 1862. 



