302 T. Davidson — Notes on Continental Geology. 



In a letter recently received from M.Coquand, tHat gentleman 

 states : — 



" I quite understand the difference in opinion which geologists entertain relative 

 to the divisions of the Chalk, or Cretaceous system, but I cannot conceive why they 

 should refuse to see what really exists. How is it? because, in France, we do not 

 possess the Hastings sands or the Tilgate beds, should we deny their existence in 

 England? Such would be neither logical nor philosophical. With reference to my 

 Cretaceous stages, is it not true that the sands of Kouen (my " Carentonien") are 

 situated above tlie beds with Pecten asper ? If geologists should call the first " Upper 

 Cenoraanien," and the second "Lower Cenomanien," they would correspond to my 

 divisions; no other change would be effected but the rejection of my names. It 

 would be possible (likewise from the same motive) to efface the terms " Bradford 

 Clay," " Cornbrash," " Fuller's Earth," etc., and to say instead Lower, Middle, and 

 Upper Great Oolite. Is it. or is it not true, that above the bed with Inoceramus 

 labiatus (Inferior Lower Chalk), and under the Upper Chalk with Belemnitella 

 mucronata we possess in Provence— 1st, thick beds with RadioUtes himbricalis and 

 Eadioliles cor nu- pastor is; 2nd, 300 metres of sandstone (Gres d'Ucliaux) ; 3rd, 

 150 metres of limestone with three forms of Mippurites, which are wanting both 

 in England and Paris. Since such is the case, we cannot help admitting it; 

 and if all this assemblage does occur in the South of France, it must result, 

 that in a general classification of the system one cannot suppress these beds. 

 I am aware that I shall be answered that the Turonien or the Craie Marueuse 

 would correspond to the above-named assemblage of beds ; but as this assemblage 

 lies in Provence above the bed with Inoceramus labiatus and under that with Micraster 

 eor-anguinum, the result is that the complete series of the Chalk does not exist at 

 Paris nor in the North of France, but must be seen in the South of France. Had 

 the English or Parisian geologists possessed this stage in their country, they would 

 scarcely have failed to introduce it into their series or classification, and they would 

 have been right in so doing. It is just as if one denied the existence of the Muschel- 

 kalk because it is absent in the British Isles. In a science of observation, one must 

 progress by the aid of positive facts. I defy any geologist to explain the sections iu 

 Provence by the Chalk series as found in England and in the North of France. It is 

 just as if English geologists had the pretension to include in the Speeton Clay all the 

 Lower Cretaceous divisions of the Continent. What Mr. Judd has demonstrated is 

 this, that you possess equivalents of some. Each district has its peculiar and local 

 formation, and it is there that one should seek for the type." 



I believe Geologists will concur with M. Coqnand that the com- 

 plete sequence of geological formations cannot be found or sought 

 for in any particular or limited district, and that in all sound general 

 classifications one must take into consideration those deposits which 

 may be present in different parts of the globe, and, as far as such a 

 thing is possible, locate them into their proper stratigraphical posi- 

 tion. We must, however, carefully avoid too minutely dividing and 

 subdividing our great divisions, for by exaggerating the number of 

 our stages we might, perhaps, be liable to fall into the prevalent 

 mistake among Paleeontologists, namely, that of forming an unneces- 

 sary number of so-termed distinct species or varieties out of one 

 great but variable specific type. 



I quite agree with M. Coquand that neither in England nor in 

 the north of France do we possess several of the etages he describes, 

 and, no doubt, with time and further consideration, we shall arrive 

 at a suitable general classification of the system, which will embrace 

 all the divisions that occur in different countries. In the meantime 

 further study of the system is urgently requisite, and many points 

 now advanced will, prior to defimite adoption, require to remain 

 open questions. 



