by Deciduous Plants in the Tertiary Floras. 297 



than the Myricea, Proteacea, and Araliacete, which abound in 

 this deposit. The same rarity of European forms occurs also at 

 Hoering, at Sotska, and at Mt.-Promina : the fact which we 

 remark at Aix is therefore not isolated ; it is related to circum- 

 stances which were uniformly repeated at the same epoch in all 

 parts of Europe. 



We are therefore led to this conclusion, — that the frutescent 

 genera of European physiognomy, and particularly the Betu- 

 lacece, Ulmacea, SalicinecB, and Acerinea, were not then distri- 

 buted as at the present day, and that they were destined neither 

 to play the same part nor to mark in the same way the masses 

 of the landscape. 



What, then, was really the place occupied by these plants ? 

 On this subject there are but few suppositions to be made; and 

 amongst these, one, no doubt, must express the truth. 



It is nearly certain that, at the epoch of the gypsum of Aix, 

 the species of Alnus, Betula, Populus, Ulmus, Acer, &c., did not 

 inhabit the immediate vicinity of the ancient lacustrine shores. 

 This part was reserved for species of Palms, ConifercB, Proteacece, 

 and Laurinece ; but we may, strictly speaking, remove the sta- 

 tion devoted to the European forms of plants beyond the imme- 

 diate margins, without by this excluding them from the neigh- 

 bourhood of the waters. In fact, they may have adorned the 

 banks of small streams, or the damp bottoms of the woods, or, 

 lastly, cool and northern exposures, at a sufficient distance apart 

 to prevent their shed leaves, &c., from being carried otherwise 

 than exceptionally into the deposits in course of formation. 



Nevertheless, if we admit this hypothesis as the true one, it 

 brings with it many difficulties. 



If the genera in question did really haunt the places which 

 we should ascribe to them as their habitation, it is difficult to 

 believe that they there formed great masses ; for in that case 

 their leaves, being transported by the winds or streams of water, 

 would have reached the lake in comparative abundance, at least 

 at certain times, although, no doubt, they would have left more 

 scattered traces than the other species. It will be seen, m fact, 

 that it is to a sort of chance alone that is due the preservation 

 of an isolated species lost in the midst of others, whilst strong 

 and numerous groups, notwithstanding distance, must have their 

 leaves and fruits carried away with a certain regularity, and in 

 such a way as to leave their impressions, perhaps not abundantly, 

 but more or less repeated. Now we have seen that this is not 

 the case with the species of European physiognomy belonging 

 to the flora of Aix. The remarkable preservation of the impres- 

 sions belonging to this category of plants is also opposed to our 

 full adoption of this opinion. These impressions are vwy rare, 



Ann. ^ Mag. N. Hist. Ser. 3. Vol xii. 20 



