Foreign Geologists : Belgian School. 577 



Gault, and third, the Upper Greensand (Craie chloritee), and the 

 White Chalk ; and he estimates that in this triple succession of de- 

 posits, the Ammonites gradually decrease according to the numbers 

 seventy-five, forty-two, and twenty-seven, to disappear finally with 

 the uppermost chalk or Maestricht beds, and before the tertiary 

 epoch. 



The total number of determined species of Ammonites in the gi'eat 

 cretaceous system of France is 144, according lo M. d'Orbigny, and 

 with the exception of three, which are common to the Gault and 

 the Upper Greensand, all the other species are divisible into groups, 

 each of which is peculiar to one of the three great divisions of this 

 system, and may be considered characteristic of it. Although the 

 species have been thus replaced several times during the cretaceous 

 IJeriod, there exists, however, among them a certain affinity of forms 

 which differs sufficiently from the general characteristics of the Juras- 

 sic Ammonites to constitute the beds containing them a truly distinct 

 and separate series. We may congratulate M. d'Orbigny on having 

 begun his ' Palaeontology ' with the fossils of this period : for whilst 

 the labours of the English, particularly the admirable general views 

 and detailed descriptions of Dr. Fitton, and the works of Dr. Mantell, 

 have contributed to a good acquaintance with the northern chalk and 

 greensand, it must be confessed that there is ample room for research 

 in the southern type. 



In consequence of the numbers of fossils sent to M. d'Orbigny 

 from all parts of France, and which I had the pleasure last spring 

 of seeing on his tables, a new light may be thrown by the ' Paleon- 

 tologie Fran9aise ' on the classification of the sedimentary masses of 

 tlie Alps and Apennines; the limestones of Greece, Turkey in Eu- 

 rope, Palestine, the coasts of Africa and in fact of the whole circuit 

 of the Mediterranean, the chief formations of which are at present 

 arranged in the cretaceous epoch. 



I might now notice the recent labours of M. Rozet, M. Leymerie, 

 M. Roliand du Roquand, M. Duval and others, whose memoirs have 

 been partly published in the volumes of the Geological Society of 

 France, but such duties pertain to the office of the President of the 

 Frencli Society, and doubtless, the eminent man* who is now at the 

 liead of it will do ample justice to these authors. 



BELGIAN SCHOOL. 



In Belgium, the most important works that claim our attention 

 for the year 1841, are, — 1st, the comjiletion of the field survey of the 

 Geological Map of Belgium Ijy M. Dumont, which was ])c'gun more 

 than four years ago, and has Ijcen pursued witii tlie zeal aiid ability 

 mauifosted by the author in his first publication, and which we had 

 so nmch pleasure in rewarding witii our Wollaston Medal. I learn, 

 however, that tlie appearance of the map may be delayed in con- 

 sfcjuencc of the time necessary to complete its engraving : 2ndly, 

 I may notice a great palijeontological work, undertaken by M. do 

 Koninck, several plates of which I examined last spring in Paris. 



• M. Cordier. 



