﻿76 Notices of Memoirs — Prof. Sehert — Folds of the Chalk. 



folds in the Chalk of Northern France, running in a general direction 

 from S.E. to N,W. These folds, five in number, he distinguished as 

 the axes of Perche, the Seine, Bray, Bresle, and Artois.^ These are 

 crossed almost at right angles by a second set, also nearly parallel, 

 whose general direction is consequently about S.W. — N.E. To 

 describe this second series, and to advance some general views on the 

 probable age of the folds in both, is M. Hebert's object in the paper 

 under consideration. 



The first fold of this second series starts at Eouen, and runs in a 

 straight line through Aumale to Pecquigny, whence it is prolonged 

 in a N.E. direction, passing a little to the south of Arras towards 

 Douai and Tournay. 



The second brings the Glauconitic Chalk to the surface at Pres- 

 sagny I'Orgueilleux and La Madeleine, near Vernon, and passes in 

 its north-east extension close to Breteuil (Oise), cutting the axis of 

 Bray a little to the south of Ville-en-Bi-ay. If prolonged in a south- 

 west direction, it would pass between Evreux and Conches by the 

 important fault which has determined the outcrop of the Glauconitic 

 Chalk in the valley of the Iton. 



The third fold runs along near the shores of the Channel. Start- 

 ing from Petreval, near Fecamp, it extends with a curve, or bend, to 

 Dieppe, where it is probably represented by the fault described in a 

 previous paper.^ At both Fecamp and Dieppe the beds dip at a 

 higher angle on the N.W. than on the S.E. side. Supposing it to 

 continue in the same direction on leaving Dieppe, it would then pass 

 through Beaurainville, north-west of Hesdin, intersect the axis of 

 Artois at Fruges, and terminate at Dennebroeucq, where the 

 Devonian beds crop up. 



The presence of these several folds leads the author to conclude, 

 in opposition to several eminent English geologists, that one, if not 

 more such folds exist in the bed of the Channel, which will offer 

 serious obstacles to the construction of a tunnel in the Chalk as 

 proposed. That such imdulations do exist there, he considers to 

 have been conclusively proved by the soundings conducted by 

 MM. Potier and De Lapparent. One of these (the fourth of this 

 series) would be nearer to the English than the French shore, but 

 parallel to the Sandgatte coast, and consequently to the other three. 



The fifth and last of the series is also the southernmost. Com- 

 mencing at Ferte -Bernard, it stretches in a N.E. direction, past 

 Beynes to Compiegne, and is exactly parallel to that between Vernon 

 and Breteuil. 



Eespecting the ages of the folds of both the S.E.-N.W. and S.W.- 

 N.E. series, M. Hebert comes to the following conclusions : — 



1. The first, or oldest, is the synclinal fold, in which the Wealden 



1 The correspondence of some of these axes with others on this side of the Channel 

 had ah-eady been pointed out by M. Ch. Barrois in a communication read before the 

 same Society in March, 1875. Thus the axis of Artois is probably represented by 

 that of Kingsclere; the axis of Bresle by that of Winchester; and the axis of 

 Bray by that of the Isles of Wight and Piu-beck. 



2 Bull. Soc. Geol. de France, 2^ serie, torn. xxix. p. 586, and ihid. 3^ s^rie, torn, 

 iii. p. 526. 



