DESHAYES ON THE FOSSILS OF THE PYRENEES. 113 



and of M. Bertrand Geslin in the Alps ; and next, that the species 

 collected by Mr. Pratt, although, belonging to the lower tertiary 

 strata, are, for the most part, different from those of M. Ley- 

 merie. It appears indeed that the analogues of the species col- 

 lected by the latter gentleman occur in the beds of the Soissonnais, 

 while those of Mr. Pratt are most nearly analogous to the cal- 

 eaire grossier species properly so called ; and it results from the 

 comparison of Mr. Pratt's fossils with those of the cretaceous rocks, 

 that there are two species perfectly identical. One of these belongs 

 to the genus Spondylus, and has been described under the name 

 of Plagiostoma spinosa. It occurs, as is well known, in the upper 

 chalk, and it is worthy of remark that it appears to be absent in 

 the more recent cretaceous rock of Maestricht. The other species, 

 common to the chalk and the tertiaries, is a singular coral which 

 M. Michelin, in his work on fossil corals, has referred to the genus 

 Guettardia. It is the G. stellata, the sixth variety in plate 30 

 of the work just quoted. This coral appears in the chloritic 

 (lower) chalk, and in the upper or white chalk, but, like the Pla- 

 giostoma, appears to be absent in the uppermost chalk of Maes- 

 tricht. Thus, it is now determined that there are in a tertiary 

 bed two fossil species which existed during the cretaceous period, 

 and both of them present the singular phenomenon of passing at 

 once from an inferior J cretaceous rock to the tertiaries without 

 occurring in the intermediate formations. 



My object at present is not to consider whether the two species 

 in question lived at the same time as the tertiary species. To de- 

 cide this, it would be necessary to examine them in their relation 

 to the beds with which they are associated, to estimate their abun- 

 dance, and to see, by the state of preservation of all the specimens, 

 whether they are actually in situ, — matters impossible to judge 

 of from the small number of specimens collected by Mr. Pratt.* 

 One might fairly enquire whether the mixture may not have been 

 made in the same manner as that which operates daily in the 

 Channel, where the fossil species washed into the sea by the de- 

 gradation of the cliffs become associated with the remains of the 

 species actually living in the neighbouring sea. 



The facts which I have just communicated to the Society 

 naturally afford an opportunity of answering certain objections 

 made by those geologists who reject the conclusions of zoologists 

 as applied to their science. These objections consist in the pre- 



* I am informed by Mr. Pratt, with reference to the doubts thrown by M. 

 Deshayes on the two fossils common to the cretaceous and tertiary beds, that 

 they were found in great abundance — that the specimens exhibited every stage of 

 growth — and that they occurred in several of the tertiary beds throughout a 

 thickness of 400 or 500 feet (the whole thickness of the tertiary deposit being 

 above 2000 feet). It is remarkable also that the Spondylus (Plagiostoma 

 spinosa) is found in the newer and the coral in the middle part of the tertiaries. 

 Besides the two species alluded to by M. Deshayes, the Terebratula striata 

 , of the chalk and greensand has also been found by Mr.Pratt, and this fossil, like 

 the others, is extremely abundant. — Ed. 

 VOL. I. I 



