President of the Geological Society for 1850. 5 



unabated intensity of the existing agents of change, — was 

 declared by M. Boue, some years ago, to be the great problem 

 of the day, and Sir R. Murchison has therefore devoted to its 

 consideration a large portion of his memoir. M. Boue indeed 

 announced in 1847 his own conviction that the nummulitic 

 rocks belonged to the eocene or lower tertiary period, and 

 remarked, in a paper read to the French Geological Society 

 in that year, how much delight Alexander Brongniart would 

 have experienced, had he lived to see one of his boldest and 

 most startling generalizations thus crowned with success.* 

 Alexander Brongniart had in fact declared many years before, 

 that the shells of the summit of the Diablerets, one of the 

 loftiest of the Swiss Alps, which rises more than 10,000 feet 

 above the sea, were referable to species characteristic of the 

 eocene strata of the neighbourhood of Paris. He only felt 

 considerable hesitation, he said, in assigning to them so 

 modern a date, because the overlying limestones were so 

 compact and homogeneous as to agree in lithological character 

 with much older secondary rocks. 



Several of the most animated discussions which have taken 

 place in this room since 1825, have turned, as you will recol- 

 lect, on this subject, especially when the fossil shells brought 

 by Mr Pratt from Biaritz in the Pyrenees were laid upon our 

 table. A decided opinion was then expressed by many of us 

 that the nummulitic series of that southern chain must be 

 referred to the lower part of the eocene group, as it was made 

 clear that the proportion of fossil species common to the 

 Biaritz beds and the chalk was extremely small — much too 

 few to imply a cretaceous age for the strata in question, or 

 even a zoological passage from the cretaceous to the tertiary 

 formations. They who have read with care the successive 

 numbers of the "Bulletin" of the Geological Society of France, 

 are aware how much that body has been occupied with the same 

 problem, and how steadily the evidence in favour of the same 

 important conclusion has been gaining strength. M. d' Archiac, 

 writing in 1847 on the fine collection of the Biaritz shells 

 submitted to his inspection by Mr Pratt, observed that forty- 



* Bulletin, vol. v. 2(1 Series, pp. 69, 71. 



