TRANSACTIONS OF THE SECTIONS. 105 



with orogi'apliical accidents. Traversing the country from Artois to Brittany, 

 they form elevations and depressions in tlie following order: — 1. The axis of 

 elevation extending from the Boulonntais to the Ardennes (axis of Artois of 

 M. Archiac). 2. Depression corresponding to the valley of the Somme formed 

 in the most recent beds, viz. Chalk with 3Iicraster cor-anyuinum, which ex- 

 tends from St. 'N'alery sur Somme, passing hy Amiens, Longueau, and Moreuil, 

 where it meets the chalk of Meudon in the direction of Noyon. 3. The second 

 axis from Compiegne to Breteuil, which extends by the valley of La Bresle 

 as far as TriSport, which opens out in the lower portion so as to show in the 

 hottom of the valley the chalk containing I/ioccranws lahiatus, and on the flank 

 the newer beds dipping in the opposite direction. 4. Between this upheaved por- 

 tion and that of Bray there is a depression which can be followed from Criel-sur- 

 Mer to Beauvais. 5. The axis of upheaval of the district of Bray is seen on the 

 shore of the English Channel at Biville-sur-jNIer. There the Craie Glauconieuse 

 is visible at low water. There are several faults which are visible in the clifls. 

 This upheaved portion is much larger than the preceding one, and is seen as far 

 as Dieppe, where it ends, being cut off by a fault of about 200 feet. 6. A very 

 well-marked depression exists between Dieppe and Fecamp, of which Veules 

 occupies the centre. There the chalk with 3Iicraster cor-anguinum descends to 

 the level of the sea, while both at Fecamp and Biville the Craie Glauconieuse is 

 at the same level. This depression runs parallel to the axis of the district of Bray 

 as far as Gisors, where the chalk of Meudon is seen at a much lower level than 

 the older beds found to the N.E. or S.W. 7. The ridge extending from Fecamp 

 to Meudon, by Rouen and Vernon. This elevation is accompanied by a fault 

 which, though in a somewhat broken line, still keeps a course parallel to the 

 general direction of the river Seine from Paris to Ronen. The sections show that 

 the strata have been raised on each side towards the fault between Rouen and 

 Mantes ; and consequently the valley of the Seine does not correspond to a de- 

 pression which would be the counterpart of the elevation of Bra)% The Seine 

 winds in and out, crossing the fault repeatedly. Beyond Mantes the fault passes 

 to Beynes, and is prolonged to Meudon, Bicetre, &c., where the chalk is elevated 

 and probably takes the form of an upheaved fold. 8. To the south-west of the 

 projecting mass of Beynes and Meudon a large depression exists, which seems to 

 take in the valley of the Eure as far as Louviers, and accounts for the presence of 

 Calcaire yrossier in this outlying portion of the tertiary basin. 9. To the south- 

 west of this zone, which extends from Trappes to Caudebec, the strata are up- 

 heaved, and the chalk with Inoceramus lahiatus is seen at the foot of the hills of 

 Le Perche. The sandstones of Maine crop up from under this chalk and form this 

 new upheaved fold, which has several flexures, and is followed by the fault which 

 extends from Nogent le Rotrou. 



Thus (1) Le Perche, (2) the axis of the Seine, (3) the district of Bray, (4) the 

 axis of La Bresle, (5) the axis of Artois from the Boulonnais to the Ardennes, 

 form five convex folds which are parallel and separated by depressions. They have 

 been produced by the general movements of the Paris basin, due to the contraction 

 of the earth's crust. These folds are of earlier date than the "Argile rouge a 

 silex " (red clay with flints), which covers up the eroded surfaces of the different 

 beds of the chalk, with the exception of the chalk with Belemnitella mncro>iafa, 

 which is probably of more recent origin ; for the lignites and the lower sands repose 

 at Veules, Varangeville, Criel, and St. "N^alery-sur-Somme on the chalk -withMicraster 

 cor-anf/uimmi. If denudation had taken place, it would not be accounted for by 

 supposing that the chalk with Belemnites was entirely removed elsewhere ; the 

 folds could have been augmented at a later period. 



The two sections show the perfect correspondence of the several folds ; but their 

 regularity is shown by all the observations made. They approach each other towards 

 the north-west, and do not extend to the south-east beyond a line passing through 

 Paris from south-west to north-east. The folds are much nearer to each other on 

 the coast-line than inland, where they are separated twice as much. 



Now, what becomes of these folds on the English coast ? It is certain that the 

 fifth and last of them, the a.xis of Artois and the Boulonnais, corresponds to that 

 of the Weald, and equally so that the Jurassic coast-line of Portland corresponds 



