70 GEOLOGICAL MEMOIRS. 



are also found in the subapennine tertiary beds near Siena in Italy. 

 This fact would induce us to believe that the Vienna tertiaries belong 

 to the same geological period, and on considering the agreement in 

 forms and the general aspect of the species, they are found to be per- 

 fectly identical. In truth, as at Siena, the species of ''Stichostegues' 

 prevail ; the Bulimina are abundant, so also the Cristellaria, the Ro- 

 bulina, the Polystomella, the Rotalina, the Textularia, &c. &c. ; and 

 the whole characters of the species depend on the same series of ex- 

 ternal modifications. This view of the age of the beds is confirmed 

 by the number of species, amounting to twenty-seven, or nearly twelve 

 per cent., still living in the Adriatic or Mediterranean. This is a 

 different view from that of M. Bronn of Heidelberg, who from the 

 study of the mollusca places the tertiary formations of Vienna between 

 the London clay of the English and the subapennine formations, or 

 in the miocene of Mr. Lyell*. M. d'Orbigny has not yet had an 

 opportunity of studying the mollusca in detail, and therefore refrains 

 from giving any positive opinion. 



Having given in this work the characters of all the genera which 

 he knew, together with the geological and geographical distribution 

 of the species, M. d'Orbigny concludes with some considerations on 

 the history of these minute beings and their progressive development 

 from the most ancient periods to the present. So far as then known, 

 no Foraminiferee had been observed in the Silurian or the Devonian 

 formations. They first appear in the carboniferous beds in a single 

 species, the Fusulina cylindrica, Fischer, but seem not to have sur- 

 vived their close. None are found in the Permian formation nor in 

 the Trias, nor yet in the lower Jurassic beds. They again appear in 

 the upper lias, in the marls of Saint-Maixent (Deux-Sevres) and of 

 Tuchan (Aude), in which he finds five species of the most simple 

 forms. In the lower oolite again none are found, but eight species 

 appear in the coralline beds (couches a polypiers) of E,anville (Cal- 

 vados) which belong to the upper part of the great oolite or the Ba- 

 thonien. In the Oxford beds again none occur, but they are pretty 

 numerous in the coralline rock above, but again disappear in the Kim- 

 meridge and Portland groups. On the whole, in the Jurassic forma- 

 tions only five genera, Nodosaria^ Vaginulina, Webbina, Cristellaria 

 and Rotalina, are found. 



In the cretaceous formations new forms and species immediately 

 appear in remarkable numbers, and go on augmenting in rapid suc- 

 cession. Instead of the five genera of the Jurassic rocks, the creta- 

 ceous contain thirty-two, of which eight are peculiar to them, having 

 never been found either in the tertiary strata or recent. To the two 

 orders of the Stichostegues and the Helicostegues found in the former, 

 representatives of the Entomostegues and Enallostegues are now added. 

 The whole order of the Agathistegues or Milioles are however want- 



* In a notice of this work in his Journal, Prof. Bronn maintains his former 

 opinion, at the same time stating that he has always considered the upper and 

 middle tertiary formations as far more closely connected than the middle and 

 lower, and that he has been confirmed in this by Grateloup's recent account of 

 the nature of tlic beds near Bordeaux. 



