of Geological Periods. 277 



Madagascar, Bourbon, and the Moluccas, do not in any case 

 quit the intertropical zone. Strictly speaking, some doubt may 

 attach to certain of these determinations considered separately ; 

 but the coexistence of such numerous indications can hardly fail 

 to render it nearly certain that true Pandanese existed in Europe 

 during the Cretaceous period, and consequently at the same 

 epoch a mean temperature of at least 20° C. ( = 68° F.). 



To give a better notion of the progress and ultimate decline 

 of tropical types in the Tertiary epoch, which I now approach, I 

 shall divide it into eight successive horizons, conceived chiefly 

 from the point of view of the fossil floras. I shall arrange them 

 as follows, proceeding from the lowest to the highest : — 



1. The Suessonian of B^Orbigny, including Eilly and the 

 lignites and sandstones of the Soissonais. 



2. The Parisian, properly so called, including the ^' Calcaire 

 grossier '^ and the London Clay. 



3. The Upper Eocene or Ligurian of Swiss authors, in- 

 cluding the middle freshwater beds of the basin of Paris and 

 the sands of Beauchamp, with beds of Cyrena semistriata, — that 

 is to say, the age of Palaotherium. 



4. The Tongrian or Oligocene, corresponding to the age of 

 the sandstones of Fontainebleau. 



^, 1l\\q Lower 31iocene, corresponding to the limestone of 

 La Beauce and the Aquitanian of Swiss authors. 



6. The Upper Miocene, including the Marine Mollasse of 

 Switzerland and Provence, up to and including CEningen. 



7. The Pliocene, from CEningen to the close of the Tertiary 

 period. 



8. The Quaternary. 



The following is an enumeration of the tropical genera be- 

 longing to each of these horizons, starting from the oldest : — 



First Horizon : Travertins of Sezanne and sands of the Sois- 

 sonnais. 



Ferns, CYATHEiE : Alsophila, Bronn. Polypodites thelypteroides, 

 Brong. Pecopteris Pomelii, Brong. Cyatheites, sp. plu- 

 rim?e. (Sezanne.) 

 Palms: Flabellaria, Sternb. — F. Goupili,Wixi., F. suessionensis, 



Wat. (Soissonais sands.) 

 Pandane/E : Carludovicat, 11. &P. — C. sp. nov. (Sezanne.) 

 AMPELiDEiE : Cissus, L. Vitigene cissoides, Sap. (Sezanne.) 

 STERCULIACE.E. — StercuUo, L., S. sp. nov. (Sezanne.) 



The genus Alsophila being indicated with certainty for the 

 Ann. ^' Mag. K Hist, Scr. 3. Vol. xix. 20 



