Secondary and Tertiary Fossil Plants. 225 



Pterodactyl, is not unimportant, as it proves that there was 

 nothing in the atmosphere so favourable to the predominance 

 of gymnosperms and to a rich reptilian fauna, which was fatal 

 to the existence both of monocotyledonous and dicotyledonous 

 angiosperms. 



You are aware that in many localities in the neighbour- 

 hood of Paris there is a formation called the pisolitic lime- 

 stone, intermediate in position between the white chalk and 

 the oldest eocene tertiary, and that there has been much 

 controversy whether it should be referred to the cretaceous 

 or to the eocene period. That it belongs to the age of the 

 Maestricht chalk seems to be the preferable opinion, and 

 some have considered the limestone of Sezanne near Paris 

 to be of the same age ; while others regard the latter as 

 lower eocene. In this limestone we have a species of Hepa- 

 tica, the Marchantia Sezannensis, Brongniart, preserved in a 

 kind of travertin, with a species of moss. How rarely must 

 we expect such discoveries to be made in rocks of such 

 ancient date ! If occasionally we obtain a glimpse of the ex- 

 istence of a lichen, a Jungermannia, or a moss, in travertin 

 or amber, it is all the evidence we can look for of whole 

 families of plants which may have played as great a part 

 in every successive geological epoch, as now in the living 

 creation. 



The number of plants hitherto obtained from tertiary strata 

 of different ages is very limited, but is rapidly increasing. 

 They*have been met with chiefly in isolated spots ; and all 

 those examined by M. Ad. Brongniart, even the pliocene 

 fossils, are considered by him to be distinct from living 

 species. They are referable to a much greater variety of 

 families and classes than the same number of species taken 

 from secondary or palaeozoic formations, the angiosperms bear- 

 ing the same proportion to the gymnosperms and acrogens 

 as in the present vegetation of the globe. This greater 

 variety may doubtless be partly ascribed to the greater variety 

 of stations in which the plants grew, as we have in this 

 instance an opportunity, rarely enjoyed in studying the 

 secondary fossils, of investigating inland or lacustrine de- 

 posits, accumulated originally at different heights above tlie 



