244 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the former, however, being reduced to one-third of the thickness he gives 

 to it on the north of Douai. (PI. VIII. Sect. 2.) 



South of this district extends j^art of the great Chalk -plateau of Picardy, 

 rising to an average height of 300 to 500 feet, and showing only at a few 

 distant intervals small cappings of Tertiaries. Of this district we only 

 possess a very general description. A little to the east, however, of this 

 line of section, between St. Quentin and Peronne, M. Elie de Beaumont 

 has given {op. cit. p. 112 and pi. 7. fig. 1) a section which is of considerable 

 interest, inasmuch as it shows that, whereas at Mons-en-Pevele the Lignite 

 series is separated from the "Lits Coquilliers" and "Glauconie moyenne" 

 by 150 feet of London clay, at the hill above Marteville, near St. Quentin, 

 the London clay is apparently wanting, and the total thickness of the 

 strata beneath the Glauconie moyenne is thus much reduced (see PI. VIII. 

 Sect. 2). The following is an abstract from the text (p. 113) : — 



Sand with calcareous concretions, full of Nummulites and Turritella... 10 to 13 

 Greenish laminated clay, containing vegetable impressions and capped 



by a seam of imperfect Ugnite 26 to 32 



Thin seams of red, yellow, and black clays, with indications of lignite : 



— a few decimetres. 

 Quartzose sand with green grains, the lower part greener than the upper. 



The thickness of the last bed is not given, but from the general descrip- 

 tion, the section, and the height of the hill, and as at a short distance 

 lower down the hill the Chalk crops out, I should suppose it not to exceed 

 20 to 30 feet. Now I presume these upper sands belong to the Glauconie 

 moyenne (Graves), with the Nummulites planulatus, and that the clays, 

 lignites, and greenish sands belong to the Upper Landenian or the Woolwich 

 and Reading series. 



The department of the Somme has been more fully described by M. 

 Buteux, according to whom the Tertiary outliers set in again more conti- 

 nuously in the neighbom'hood of Montdidier. He gives the following 

 section on the chalk-hills between Davenescourt and Hangest : — 



feet. 



" Grey sand and thin seams of sandstone 2 



Reddish sand 6^ 



Greenish sand 9| 



Whitish sand ?" 



It is on the confines of the Somme and the Oise that the remarkable 

 thick pebble-beds, extending from east to west, and which M. Graves 

 (p. 182) considers as indicating the bovmdaries of an old shore, occur. On 

 Mont Soufflard, between Montdidier and Breteuil, these beds are largely 

 developed. M. Buteux gives the following section of them : — 



feet. 



" Round flint-pebbles enveloped in a matrix of grey plastic clay* 25 



Grey and yello's^'ish plastic clay, with rare remains of shells 4 



Sandy bluish grey clay 4 



Lignites 6^ 



Bluish plastic clay 4 



Whitish sand passing into greenish 16 



Plastic clay ?" 



M. Graves gives the following section of the hill-top at Coivrel, south 

 of Montdidier : — 



reet. 



" Yellowish and ferruginous sands with sandstone 23 



Compact green clay 2 



* According to M. Graves (p. 243), it is — sands and pebbles 26 feet. The 

 shells beneath he states are the Ostrea Bellovacina and Paludina lenta. 



