296 Count Gaston de Saporta on the Part played 



appear to be a last vestige of an ancient type on the point of 

 disappearing, rather than an essential element of the vegetation 

 of the north of the two hemispheres, as are the Betulacea, Sali- 

 cinece, Cupuliferce, and Ulmacece. If we limit our remarks to 

 these last groups, adding to the species above cited those which 

 enter into the same category, such as Alnus antiquorum, Sap., 

 and Ostrya humilis, Sap. (although the leaves of the former were 

 no doubt persistent, like those of Alnus nitida, Spach, its Ne- 

 paulese analogue, and the involucra alone of the latter are known), 

 we shall obtain a total of ten species actually representing the 

 boreal element of the flora of the gypsum of Aix, — all these 

 species, as has been said, being extremely rare in individuals. 

 This rarity is the more remarkable because, if we consider the 

 present importance of these organisms, and even that which 

 devolved upon them in the latter half of the Tertiary period, 

 they are amongst the most generally distributed species, for the 

 natural reason that most of them, and especially the species of 

 Alnus, Populus, and Ace)', frequent the margins or the vicinity 

 of water— a circumstance which must have favoured the pre- 

 servation of their shed leaves. 



To be convinced of this, all that is necessary is to glance 

 through the principal fossil floras, starting from the true Mio- 

 cene. Betula Dryadum, Brongn., in company with an Acer, has 

 filled with its fruits and leaves the strata of Armissan (Aude). 

 The two, no doubt, covered the Secondary slopes in the neigh- 

 bourhood of the lacustrine basin in which are deposited the 

 flags with impressions which are quarried in that locality. At 

 Manosque Alnus nostratum, Ung., and Carpinus grandis, Ung., 

 are amongst the commonest species. In the Swiss Mollasse 

 deposits this is the case with the species of Alnus and Carpinus, 

 and next with those oiPopulus, Salix, Platanus, and Liquidamhar ; 

 at ffiningen, Pojmlus latior, A. Braun, and Acer trilobatum, A. 

 Braun, are seen on every slab, in company with several species 

 of Salix. Nothing is more natural than the abundance of these 

 forms in reference to the present condition of things ; but no- 

 thing is better established than their rarity as soon as we descend 

 the series of beds and approach the Tongrian. At Saint-Zacharie* 

 Alnus prisca, Sap., Betula ulmacea, Sap., and Ostrya tenerrima, 

 Sap., are very thinly scattered; Acer j)rimavum, Sap., and Car- 

 pinus cuspidata, Sap., are more abundant, but still much less so 



* The actual age of this flora, at one time referred back by us, with 

 doubt, to the Bartoniau (see ' Recherches sur le Chmat et la Vege'tation du 

 Pays Tertiaire,' par O. Heer, traduit par C. T. Gaudin, p. 135), has since 

 been found, after fresh explorations, to be less ancient than the gypsum of 

 Aix, and not very distant from that of Hoering in the Tyrol, a Tongrian 

 locality. 



