232 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



have been described, although a few have been found in Belgium; 

 but the mass, position, and mineral character of this bed of clay leave 

 little doubt of its identity with the London Clay. To M. Dumont is 

 due the merit of first having pointed out the analogy of his Systeme 

 Ypresien with the London Clay proper. 



§ 9. Lower Bagshot Sands ; Systeme Ypresien superieur or Sables 

 Ypresiens ; Lits Coquilliers and Sables divers, or Glauconie 

 moyenne. 



Having shown in a former part of this paper that the Lits Coquil- 

 liers are somewhat more nearly related to the '* Calcaire grossier " 

 than to the marine beds associated with and underlying the " Argile 

 Plastique," whereas the London Clay proper shows, on the contrary, 

 closer affinities with these latter beds, it remains to be ascertained 

 whether we can in any way prove the superposition of the Lits Co- 

 quilliers and associated sands on the London Clay. I believe that 

 this now admits of proof, and that in this country the Lower Bagshot 

 Sands form the equivalent beds of the Glauconie moyenne. 



The hill of Cassel, about thirty-five miles E.S.E. from Calais, rises 

 to a height of 515 English feet above the sea, and affords some in- 

 teresting sections of a large portion of the Belgian series. At about the 

 middle of the hill are some calcareo-arenaceous beds, in which M. Elie 

 de Beaumont many years since found the Cerithium giganteum and 

 other shells which induced him to refer those beds to the zone of the 

 " Calcaire grossier." The correctness of this parallelism has been 

 generally admitted, and has been confirmed by the observations of 

 M. d'Archiac*, who further proved that these beds were underlaid 

 by fossiliferous sands which he referred to his " Lits Coquilliers," 

 and tracing the same zone to Brussels, he showed that it was there 

 characterized by that most abundant fossil of the French beds — the 

 Nummulites planulatus. 



These correlations have been since adopted and extended by 

 M. Dumont and Sir Charles Lyell ; the latter of whom further gives 

 a measured section of the hill of Casself, which, with the list of 

 organic remains he likewise furnishes, afford the exact data we require 

 for comparing these beds with others in this country. We need not 

 at present notice the upper part of the hill, which to the thickness of 

 about 120 feet is composed of the sands of Diest, and of the Laeken 

 beds with the Nummulites variolarius. Beneath these strata is the 

 zone before-mentioned and referred to the " Calcaire grossier." But 

 the change, both in mineral characters, importance, and the fauna, 

 between the beds of this age at Cassel and in the Paris district is very 

 great. Instead of the thick mass of soft earthy limestones with 

 subordinate green sands (" Glauconie grossiere") at their base, 100 

 to 150 feet thick, and containing a rich fauna of 600 to 800 named 

 species, we have at Cassel a series of beds consisting essentially of 

 mixed yellow and green sands more or less pure, and of very thin 

 subordinate beds of sandstone usually with a calcareous cement. 



* Bull. vol. X. pp. 183, 193, 1839; Hist, des Prog. vol. ii. pp. 497 & 500. 

 t Op. cit. p. 324. 



