556 J. F. BLAKE ON THE UPPER 



Pig. 15— Map of Part of the Pays de Bray. (Scale 1 : 240,000.) 



grit above discussed, they are not much thinner. The upper portion of 

 this, in which the lumachelles and the intervening material become 

 very sandy, requires more discussion. M. de Lapparent says : — "At 

 the top of this system the lumachelles grow together into solid banks 

 intercalated with very sandy material, and forming rather irregular 

 masses than continuous beds." These sands and doggers are well 

 seen to the north of Louvicamp. The sand is pure; and the doggers 

 are huge ; and at the top is a lumachelle of Trigonice, which appear 

 to be T. Munieri. "We have therefore the exact representative of the 

 sandy beds at Gris Nez and Mt. Lambert in the Boulogne area. The 

 same is exposed in the railway-cutting south of Haussez, where the 

 beds seen are 10 feet or 12 feet of grits and sands, thickening to the 

 south, and with abundance of Exogyra virgula. The presence of this 

 last fossil may at first appear a stumbling-block; and it undoubtedly 

 proves the close connexion of these rocks with the Virgulian ; yet, 

 when we compare the Boulogne district, it proves nothing, since the 

 species is equally abundant in the sandy beds which in that area are 

 referred to the "Lower Portland;" on the other hand the penological 

 similarity is of great weight. Overlying these comes the " Compact 

 Lithographic Limestone," a rock which can be scarcely be matched 

 either in England or at Boulogne. It has a thickness of certainly 

 more than 12 feet, and contains lumachelles of Trigonice too deeply 

 imbedded for the species to be recorded. At Louvicamp it has also 

 lumachelles of Exogyra virgula. The two fossils mentioned by M. de 

 Lapparent are Ammonites cf. gigas, too characteristic a fossil to be mis- 

 taken, and Gervillia Icimmeridiensis, which might well be G. linearis, 

 so similar are the species of this genus. Next comes another mass of 

 clays which are said to be likewise 200 feet thick in the south, but are 

 certainly not so much in the central portion, where examined. There 

 are few fossils in them beyond Exogyra virgula, which occurs in luma- 

 chelles. It is seen underlying the cement-stone beds of the cutting 

 at the station of Saumont-la-poterie. These cement-stones are 

 regarded by M. de Lapparent as forming the base of the " Lower 

 Portlandian ; " and he states that Exogyra virgula is entirely and 

 suddenly replaced in them by Ex. catalaunica. This is certainly 

 not the case : after the cement-stones begin there are no more 

 lumachelles ; but Ex. virgula occurs in tolerable abundance in the 

 marls above, at least 6 feet of them. This fossil, therefore, is no 

 more available here for drawing a line at the base of the " Lower 



