114 GEOLOGICAL MEMOIRS. 



tending that when certain species are troublesome to zoologists, 

 they unite them as varieties, separate them into distinct species, 

 or declare them new, in order to make their distribution agree 

 with a pre-established division of formations ; so that, acting in 

 this way, (it is said) the Palaeontologists turn their science into a 

 convenient system, always ready to adapt itself to all phases of 

 observations, since the determination of fossil species, on which the 

 most important results of the application of Zoology depend, is 

 guided by no fixed principles, and seems exposed to the caprice 

 of every observer. 



If the works of some Palaeontologists have deserved these ob- 

 jections, no such reflection can be cast on the general application of 

 Zoology to Geology ; and I may safely say, that my own works, 

 known to the Society, are exempt from this reproach of uncertainty 

 which is frequently applied to Palaeontology ; and I believe that 

 all the comparisons I have made of species from different formations 

 have been unprejudiced. 



I would add in conclusion, that it is highly desirable that a col- 

 lection, as carefully made as that of Mr. Pratt, should be put in 

 the hands of a skilful zoologist, who might carefully determine the 

 species and give a complete list of them ; and I would have under- 

 taken this work myself if the stay of Mr. Pratt had been pro- 

 longed. I will only now say, that, besides a number of new species, 

 I have found a considerable number also of which the analogues are 

 met with at Chaumont, Parnes, Grignon, and the calcaire grossier 

 of Paris ; and it is worthy of remark that Mr. Pratt has found at 

 Biaritz several new species of encrinites which remind one of those 

 of the cretaceous period, and even of some found in the lias, as 

 well by their large size, as by their external characters. It is to be 

 hoped, notwithstanding the accuracy of Mr. Pratt's observations, 

 that they may not be the last; and no doubt our colleague, M. 

 Leymerie, will communicate to us before long the facts he has dis- 

 covered with reference to this subject in the course of the present 

 year. 



D. T. A. 



III. On the Geological Structure of the Neighbourhood of 

 Bayonne. By M. Thorent. 



[As having reference to the above, I insert a notice of a paper read by M. 

 Thorent before the French Geological Society on the same day as M. Deshayes' 

 " Memoir," and referring to the geological evidence on the same subject. Some 

 of the more important results however have been already given in a paper by 

 Mr. Pratt, of which a notice appears in the " Proceedings of the Geological 

 Society," vol. iii. p. 157. En.] 



The opinions of authors on the geology of the neighbourhood of 

 Bayonne have been very various and discordant ; some affirming 

 that the sandy calcareous beds of Biaritz belonged to the cretaceous 



