﻿1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



even a tree-fern has been detected in the ferruginous sand of the 

 lower cretaceous group in the Ardennes in France. Yet this vegeta- 

 tion is referred by Brongniart to the age of angiosperms, some 

 well-marked leaves of dicotyledonous trees having been found in 

 Germany, in the cretaceous quader-sandstein and planer-kalk. The 

 co-existence of these with numerous cycads and with the great rep- 

 tiles, the Iguanodon, Ichthyosaurus, Plesiosaurus, and Pterodactyl, is 

 not unimportant, as it proves that there was nothing in the atmo- 

 sphere so favourable to the predominance of gymnosperms and to 

 a rich reptilian fauna, which was fatal to the existence both of mono- 

 cotyledonous and dicotyledonous angiosperms. 



You are aware that in many localities in the neighbourhood of 

 Paris there is a formation called the pisolitic limestone, intermediate 

 in position between the white chalk and the oldest eocene tertiary, 

 and that there has been much controversy whether it should be re- 

 ferred 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 f 

 In this limestone we have a species of Hepatica, the Marchantia Se- 

 zannensis, 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 existence 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 spe- 

 cies taken from secondary or primary formations, the angiosperms 

 bearing 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 



