of Geological Periods, 347 



those corresponding to them in the present state of things is 

 truly surprising. 



The third horizon, composed chiefly of the flora of the gypsum 

 of Aix, brings out this phenomenon still more strongly. In it 

 we find the following European genera, taking into account the 

 most recent observations : — 



Alnus antiquorum. Sap. Cornus, sp. ? 



Betula gypsicola, Sap. Hedera, sp. 



Ostrya humilis, Sap. Acer ampelophyllum. Sap. 



Quercus salicina, Sap. Crateegus nobilis. Sap. 



Ulmus plurinervia. Sap. Cercis antiqua, Sap. 



Populus Heerii, Sap. 



More than half the genera that figured in my list appear to 

 have disappeared in the period extending from the Middle Mio- 

 cene to the Upper Eocene. Those which remain are represented 

 in each locality only by a very small number of species, or even 

 by a single one. Most of these species, however, are very well 

 characterized, and known by their fruits as well as by their 

 leaves. The fruit of Ulmus plurinervia, lately found by M. 

 Marion, indicates a species very nearly allied to our U. campes- 

 tris. The leaves of Crataegus nobilis are hardly to be distin- 

 guished from those of our hawthorn. Cercis antiqua diff'ers but 

 little from our C. siliquastrum ; but Betula gypsicola, from the 

 examination of its leaf, would resemble the smallest forms of its 

 genus ; whilst Populus Heerii resembles P. euphratica, Oliv., in 

 its fruit, and P. laurifolia, Leb., in its leaf. There is therefore 

 a very considerable diversity in the mutual affinity of these types 

 with those of the present day. In general they are remarkable 

 rather by a sort of stunted condition of the foliaceous appen- 

 dages (which leads us to ascribe to them only a moderate size) 

 than by their diff'erential characters, which present nothing very 

 striking. 



I had formerly thought that the flora of Aix was really the 

 starting-point of that boreal group which we have seen reappear- 

 ing with so much persistency at all the steps of the series of 

 stages ; and what confirmed me in this notion was, that the pre- 

 vious stages did not contain any very distinct traces of it ; but 

 during the last few months my profound study of the plants 

 from the celebrated locality of Sezanne, belonging to the stage 

 of the sands of Rilly, has compelled me to abandon this opinion. 



In fact, in this the oldest known flora of the Tertiary epoch, 

 I have observed, in the midst of a multitude of Dicotyledons of 

 exotic physiognomy, and very difficult of determination, traces 

 of a portion of the European genera the progress of which we 

 have just followed; and among these I have even met with some 



