JUEASSIC OF THE PARIS BASIN. 



555 



parent (69), published as one of the memoirs of the Geological 

 Survey of France. Only a small portion of the Upper Jurassic 

 rocks is exposed in this district, brought up to day by a N.W. 

 and S.E. elevation, from the summit of which the Cretaceous rocks 

 have been worn away. It thus affords, as it were, a continuation 

 of the coast-section of Normandy, commencing at the base where the 

 latter ceases, namely in the Virgulian marls. M. de Lapparent 

 classifies the rocks thus exposed as follows : — 



Upper Portland. 

 Ferruginous sandstone, speckled clays, greensand. 



Middle Portland. 

 Blue marls. 



Lower Portland. 



1 . Upper conglomerate. 



2. Grlauconitic calcareous grit. 



3. Marly limestones. 



4. Calcareous grit with Anomice. 



5. Beds with Ostrea catalavnica. 



KlMMERIDGIAN. 



1. Upper clays and lumachelles. 



2. Compact lithographic limestone. 



3. Lower clays and lumachelles. 



4. Calcareous grit (Pterocerian or Astartian ?). 



The accuracy of this description has been verified so far as may be 

 in a brief visit, and the correctness of the correlation determined — 

 with one important exception, which may be the subject of discus- 

 sion. According to verbal communications from M. de Lapparent, 

 borings executed between the Pays-de-Bray and Boulogne have 

 shown Cretaceous rocks lying directly on Palaeozoic ; so that we are 

 not led to expect the Jurassic rocks to be continuous between the 

 two districts. Nevertheless, as we have seen, the lower portions of 

 the deposits under study are remarkably similar to those of England ; 

 and as the true Portland rock of England reaches to Boulogne with 

 little change, we may expect the intermediate beds to be also similar 

 to those of England and differing from them in the direction of 

 Bolonian characters. Judged in this way, the so-called " Lower 

 Portland" (used in the Bolonian sense) of the Pays-de-Bray should 

 begin to show its episodal character somewhat lower in the series. 



The lowest bed visible, the sandy calcareous grit, is a very 

 doubtful rock, seen only at one place. One cannot be sure that it is 

 in situ ; and its badly preserved Trigonice and Astartce suggest that it 

 may be a mass belonging to No. 3 of the " Kimmeridgian." In any 

 case it has no particular 1 resemblance to the Trigonia-grit of Havre, 

 and cannot lead to the inference that we are here low down in the 

 Kimmeridgian, as we should be if it belonged to the " Pterocerian 

 or Astartian." The "Lower Clays and lumachelles" with Exogyra 

 virgula present nothing worthy of note, except that towards the 

 south they have a thickness of 200 feet, and on the opposite side of 

 the same valley between Louvicamp and Mesnil, which contains the 



